From my point of view, Toshinori is a great inspirer but a rather mediocre teacher, lacking the instinct for teaching and sensitivity to people and empathy from the start. (But he began to learn this when he retired). In a sense, he is an individualist: he counts only on himself and his own strength, does not accept help from outside (unless the situation forces him to accept help), is independent in his views on life and actions, puts his own interests above the interests of others.

Let's break down each of the points I wrote above.

1. He counts only on himself and his own strength. Toshinori grew up in a time of an active criminal community, when neither heroes, much less authorities, could cope with criminal activity. So Toshinori decided that ordinary people and people who have the power and the ability to change anything have no confidence in their own abilities, no beacon to guide them to the light. Who else but him! And he decided to be that beacon. A symbol of Peace. A bit selfish, isn't it? But this ambition captivated Nana, and she decided to help realize his goal.

And herein lies Toshinori's first mistake - becoming the Symbol that everyone will rely on. One person is the hope of most people. One person will do everything in his power for the good of others.

This is the fault of the very concept of “One for All” - the power is given to one person to defeat evil himself. Yes, it seems that this power is passed from one to another, but this person usually works alone, continuing the work of his predecessors.

You might counter that AFO hunted down the OFA’s successors, killing their loved ones and friends, so all the successors are forced to be loners to protect their loved ones. Yes only Gran Torino is still alive, although he was a very close friend of Nana and mentor of Toshi. There are also various archival records of En, Banjo and Shinomori. Someone must have led them, known these people, perhaps even intimately. That is to say - friends and acquaintances of the Predecessors are probably alive by the beginning of story. It is a little strange for the image of universal evil presented not to try to take advantage of these loved ones of their adversaries, who certainly were not hiding, just to leave no information about them.

Because the OFA's successors all embraced the idea of a one-man battle. That only they - and no one else. Only one person fights for everyone. Honestly, an absolutely stupid concept, Afo would be smarter on this point - a real and lasting result can be achieved by a group of people united by one idea. Yes, he manipulates people, controls them in different ways. But there is an Idea, there are people united in a group who work (even if sometimes against their will) to realize it. Teamwork, in a way, where you have to reckon with other people's strengths as well. (But Afo is a separate issue, because even though he does a lot with the hands of others, he still prefers to reassure himself, in order to be sure of the result - you have to do a lot yourself).

And getting back to teaching. What did Toshinori say to do to Izuku? Clear the beach by himself. He also set a strict time limit. Yes, you'll say it's such a workout for him, plus a good deed for society. And the time limit is neat before the entrance exam. However. The food and training system has been worked out, and Toshi was only present during these training sessions when he was not doing heroics and other activities related to fame. Also, don't forget that Yagi Toshinori has an official job as the personal secretary of All Might, who must attend management meetings as the Hero's representative. Which means that Izuku was left to himself, again. When next to him there should have been a teacher, who would have shown him how to redistribute mass correctly so as not to get injured; or the correct technique to perform any techniques: properly placed legs, body tilt, raised arms, position and strength of fist clenching before, during and after blows (believe, this is a very important aspect in hand-to-hand combat, which allows for maximum impact effect and preservation of own body. It's not just mindlessly punching with your hands and feet, putting all the available force into the punch.) Of course, working on your own is good, but giving at least the basic basics to Izuku was a must. And in the end, he got it into the boy's head that he had to do everything himself and not rely on anyone else. (Toshi was upset that Izuku left him and went off on his own. Sorry, but you reap what you sow.)

And please note: the Takoba Beach situation is very revealing - it is an allusion to contemporary hero society. The problems in this society have been piling up for years, like trash on the beach. People simply turned a blind eye and did not want to see it. Perhaps Someone tried to do something, but only talked and then quit. And only one person was entrusted with clearing it up on his own: a young boy with burning eyes. And he single-handedly cleared the beach. And people immediately began to admire this act of an unknown hero. Except... instead of helping to clean up, people just started enjoying the end result, and who knows when the first long-lasting garbage will be there again. And then they'll start complaining that the beach is dirty again, and then they'll turn a blind eye to it. Until someone comes along who takes the responsibility to clean it up. So it is with the heroic society - everyone knows the problems: Corruption, discrimination, greed for profit instead of real action, until someone is particularly loud about the problems (villains). And then society will hold one person accountable to deal with the problem, for someone else to take responsibility for decision-making and action. But society will remain infantile and angry until it is fed a tasty treat that will calm it down for a while. The problem will not be solved, though-until society's very thinking changes from “someone alone” to “all together”.

2. Not accepting outside help until forced by circumstances. All Might always worked alone, only once did he have a full partner: Sir Night Eye (David Shield was more technical support than partner). And then, for the most part, Sir acted as secretary, dealing with all the paperwork that needed to be filled out and submitted for reporting. I think that's why All Might took Night Eye as a partner - just to pass the paperwork off to someone else, if the opportunity presented itself. However, the same thing happened to the police who came close to All Might, Tsukauchi in particular. Of course, because of the first point, the Symbol of Peace has no time for reporting. Of course, he could not share the area of responsibility with other top-heroes, delegating some of his cases in different regions (sarcasm).

Because people see him as a Symbol, as that Pillar to lean on, which means they need him more than paperwork. And I think that pleased his All Might's Ego very well.

But when the situation “All Might in the battle with Afo” caught up, and then with the aftermath of that battle, Toshinori would not accept Sir and Gran Torino's help and advice. Moreover, he might well not have listened to the admonition before the battle from Sir, who was a very good analyst and had a terrific quirk.

Back to teaching: based on the first point, Izuku had to clear all the debris on the beach by himself. Moreover, Toshinori had forbidden telling even his closest ones about the quirk. Yes, confidentiality and secrecy, but... that's a stupid decision, because Izuku, once he acquired the quirk, had to deal with it himself, there was no help from Toshinori - he got it right away because a) he was more physically developed and b) the quirk had become very strong over 40 years, much stronger than when Toshi got it. And his inappropriate comparison to an egg in the microwave is not to let the shell crack. Have you tried boiling an egg in its shell in the microwave, though? You'll take a long time to wash out the microwave. Because the egg’s white opens up when heated, the water evaporates, the steam has nowhere to escape, pressure builds up, and then there's a steam explosion from the inside. Even if the microwave egg hasn't exploded after the timer has passed, it will explode if you break the integrity of the shell - the pressurized steam won't magically disappear. (Don't do this at home!!! Look it up on youtube!)

So it was advisable for Toshi to tell someone who knows a thing or two about teaching or running a quirk that he has an successor and needs help. But no. Gran Torino himself approached the Academia to take Izuku as an intern, so as to at least teach him a little bit about quirk control. (And if Toshi hadn't been so overconfident, Izuku might well have taken first place at the festival, without serious injury. In fact, he might have mastered his quirk sooner if the other side had been involved.)

3. Independent in his views on life and actions, putting his own interests above others. Here is a very interesting point. Considering Izuku to be his big fan, who copies him, he unknowingly began to try to teach him, as Nana clearly tried to teach him, trying unknowingly to mold him into a second Symbol of Peace. In Izuku's case, there was no individual approach to teaching because Toshi had never encountered teaching and basically just copied his techniques and training. He didn't ask Izuku about what he was strong at, but although he saw the quirk's analysis notebook and even flipped through it while signing it. However... he did not develop this skill in Izuku, focusing only on physical training.

This is especially evident at the sports festival, when he explicitly told Izuku to make himself known loudly. Because All Might himself took first place in his first year of training. He set the task, gave the admonition, and sent him off to fight at the festival.

Toshinori is also quite categorical. He did not accept the motives of others until recently, clearly separating black and white, and did not ask about the situations of the villains. Only the Stain's case and perhaps Shimura Tenko's situation could have stirred something up, but as far as morality is concerned, Toshi remained black and white. Of course, this is the result of the very time he grew up in, but Nana was quite a romantic and sensitive nature who could probably also sympathize with some villains. But Toshinori saw only one way at that time: to be strong, to defeat the villains, to clear the streets of criminals so that people could live in safety without fear of being attacked from around the corner. At the time, there was no choice for him but to divide it into black and white. And that became something of a stigma in his personality later on, even in peacetime. A professional deformation of personality.

In chapter 337, when Aoyama admitted to being a villain, Toshinori's world was shattered. He believed that everyone in the A-class had a hero's heart, no one associated with villainy. He didn't even have any suspicions because they were all kids who wanted to be heroes. But the reality turned out to be brutal. Because he does not know what to do in this case, probably the kind of thing he has never encountered - betrayal among loved ones, among comrades. (Basically, all the faculty involved in the interrogation were stunned, which is surprising, if we were introduced to Nezu as a very intelligent being. And in my opinion, they lacked their own Severus Snape, who was critical of students).

And Toshi was stunned when Young Midoriya, on emotion, tried to pull the situation out, to save Aoyama Yuuga even in this position from himself. At least with words and hope for the future. I believe that at this point Toshinori was at a standstill because his usual picture of the world is no longer clearly black and white, and in fact there is a lot of gray in it. (Or, what else is possible, he didn't realize how truly bright Izuku's nature is - Izuku is emotional, but restrained and patient. The boy keeps a lot inside himself, and I don't remember a moment when he openly declared his feelings and thoughts and regrets, as Katsuki did during their fight, for example. Tears are just one way to relieve tension and dull negative emotions, to make the heart a little lighter. But there will come a moment, and everything diligently shoved into the most distant dark corners will come out into the light.)

And if you consider it in the way he teaches - the really good thing here is that Izuku initially has his own morality. Not black and white, but gray. And he is very good at applying it, adjusting it, and even teaching it. And his views change, evolving with circumstances and new conditions. And this - it teaches All Might, who has faced though a fan, a man who will be his successor and continuation of his life's work, but for the most part he faces the consequences of what his successor is doing under his guidance and not. He faces precisely the resonance that Izuku's actions cause in him and in the world.

But if we compare Toshi “then” and “now”, he has grown and revealed himself very well - he continues to develop, facing villains not as an acting hero, but as the most ordinary civilian. By the way, this is one of his main conflicts, when he has to look at everything from a completely different perspective - that of a powerless man - the first chapter (series) of the story. And it is only because of the spirit that shines within Izuku that Toshinori develops precisely as a Hero - his Hero Spirit develops. Yes, the quirk allowed him to Become a Hero, but the very Spirit that was in him before getting the quirk seems to have hidden away, replaced then by revenge for Nana and a bright desire to destroy the villains. And after the first battle with Afo - it's as if he lost meaning, doing his job automatically. Because he had to.

But after the meeting with Izuku, when Izuku awakened Toshinori Yagi the Hero by his actions rather than All Might, that's when Toshi's history as a Hero began.

That incident on the roof, which a lot of people don't like, shows this well. Then it was All Might, the very image that had been created for 40 years, who told the truth - you can't become a hero in today's world without a quirk. The quirkless just won't survive; he needs safer activities. And for sure Toshinori just didn't realize that over these 40 years the attitude towards the Quirkless has changed, and he himself assesses the capabilities of the Quirkless as 40 years ago - when there were more of them and such a derogatory attitude didn't exist yet. And by the way - in this - in the attitude towards the quirkless, there is his fault - he created the image of a strong and invincible Hero, where the brightness of quirk determined his fate and the fate of people. The already strong dictate how one should live, and the strongest Hero, with the brightest and most powerful quirk - accidentally created a society in which a strong quirk decides one's fate - because everyone wanted to look up to him, and as a rule - everything was built around his image, in particular hero propaganda, media, advertising, consumer goods. The flip side of Peaceful Time.

So however cruel All Might's words were then on the roof, they were unintentional. He showed the consequences of his heroics clearly; and what would heroism do to a simple boy without a quirk? However... he remembered himself - the quirkless boy Yagi Toshinori, only after Izuku tried to save Katsuki - after the recklessness that almost cost both boys their lives. And you know, if it weren't for that - it's likely that All Might wouldn't have defeated Afo a second time in Kamino - after all, one of the main reasons why All Might is still alive and fighting evil is because his disciple reminded him how he was himself in the distant past, his dreams and goals, where he came from and why he took this path in the first place. (But speaking of Izuku's reckless behavior later on, this is a problem of All Might's pedagogical skills-as mentioned above.)

Yagi Toshinori is the kind of man who hopes for the best, but is afraid of the real picture of life, which reminds him of his personal losses and regrets. He held on to the story of OFA and AFO until the last moment, simply believing that it would be of no use to the boy, that everything dangerous was behind him. He procrastinated telling him about his future death - he just didn't have the guts to tell it to the boy who looks at him with stars in his eyes. He wasn't even going to talk about Togato Mirio as a possible successor. And he's also afraid to admit some things that are in plain sight - the same similarities between Afo and Izuku. And you know - being afraid to admit the obvious or tell the truth is so human. People naively believe that ignoring something will somehow make It less true and keep a false peace. Lying and remaining silent is salvation, because the truth can hurt. So it's better not to muddy the water unnecessarily, because if you're lucky, nothing will ever come out of that water.

You know this, don't you?

Yagi Toshinori is the same person, with his pluses and minuses. With his weaknesses and strengths. He is brave and daring, jumping in the face of danger without hesitation. But at the same time, he is afraid to admit the inevitable and the obvious, when it can hurt someone, cause bad thoughts, emotions, feelings. And he will naively delay the moment of an important conversation for just this reason. At first he projected it all from his side to Izuku - because he knows what it is to lose a Master, to lose a loved one whom one admires, whom one looks up to. And he knew how painful it would be. And then, when he realized - that Izuku was not that boy Yagi Toshinori, not just a fan, but a different, totally awesome person who had become more related than anyone else, that fear became even more alive and powerful. Now in addition to his own experiences wearing him down, his perceptions, so now he knows exactly how he will feel, what Izuku will think. And by the current traitor's arc - he realizes where and what he has missed in his time. He realizes where his fault is, where he should have been more sensitive, more caring, more assertive. And he admits his fear, his indecision after the fact, and now he tries to make up for it, to be better, more useful. It's just like in life.

Because “My Hero Academia” is a story about life, about people. About how people face the consequences of their actions, their words. How people change, how they go through their crises and personal conflicts. And we're not just talking about it here - this story is Alive, everyone finds themselves in the beloved character, everyone finds a response in the stories of the characters.