Very Dubious

It's not even Stratt's subjective opinion, genuinely — it's something she yells in the middle of an argument, angrier than ever before, throwing the most venomous insults into the face of the man who betrayed and insulted her.

Now, the first part, about his change of career, is more insightful, and is actually echoed by something Grace himself thought a couple of chapters before:

I missed my kids. Dozens of them. Hundreds, really, over the course of a school year. They didn’t swear at me or wake me up in the middle of the night. Their squabbles were usually resolved within a few minutes, either by a teacher-enforced handshake or detention. And, somewhat selfish, but here it is: They looked up to me. I missed being that respected.

Plus, the entire book, down to the very structure of it, is evidence of how much Grace loves working in a lab, solving problems, making discoveries. And he did give up on the career of it in favor of explaining the same things to children year after year after year. And he, as demonstrated by the quote above, does enjoy being an admired authority figure at a low-stakes workplace. It's not the full picture (I'll get to it later), but let's give Stratt this one.

On the other hand, “You don’t have a romantic partner in your life because that would mean you might suffer heartbreak” is not supported by anything in the rest of the text. The only mention of Grace's involvement in romance is a (misogynistically) contemptous memory of his college girlfriend and their “total disaster” of a relationship. He ignores Lokken's bashfulness around him, and when confronted with other people's relationships or their idea that he's in a relationship with Stratt, there's not even a smidge of wistfulness in him. He doesn't have a romantic partner because he! is! not! interested!

You could have replaced “romantic partner” with “close friend”, and even that isn't particularly true to what we see. The only time Grace represses the feeling of affection for his friends to save himself from heartbreak is at the very beginning of the book when he tries not to think about Yao and Ilyukhina, and in that case managing his negative emotions is actually a reasonable and mature decision: giving in to grief in that moment could have put the entire mission at risk.

I think this is one of the cases where the movie's script provides a clearer and more emotionally intelligent summary. “You just need to find someone to be brave for”, cut to “Who would you die for?”, cut to Rocky saying hi.

The thing is, both in the book in the movie, Grace simply didn't like anybody enough to try to get close to them, and love anybody enough to die for them, until he met Rocky.

And there are many reasons why he grew to care about Rocky more than about anyone ever before! Where do we even begin:

Even before they understand each other on a personal level, Rocky is the most interesting individual Grace has ever met just by virtue of being an intelligent alien. Of course he is more motivated to get to know Rocky than any old human!

The two of them need to establish communication from scratch. This forces Grace to recognize that the other person has an entirely different perspective from him, and put effort into understanding his partner, expressing his own perspective clearly, and making sure they're on the same page. Same on the physical level: the incompatibility between their living spaces and difference between their physiologies makes Grace more aware and considerate of someone else's needs.

Why should the onus be entirely on Grace? It takes two to tango. And you know who invites Grace to tango? Rocky does (in the movie, literally). Rocky does all the hard work at the beginning. He's the one to notice Grace, approach him, send the first message, arrange a way to meet. It is Rocky's idea for him to move in with Grace. It is Rocky who sacrifices himself to save Grace's life first, long before Grace does the same in return (or shortly before, if you count the risky airlock maneuver in the book). “I like to keep a wall up in my relationships anyways”? Rocky goes through that wall for Grace's sake, figuratively and literally. By the end, Rocky has won Grace over fair and square. Has any of the humans who ever wanted to befriend or date Grace put in a fraction of Rocky's effort?

Grace connects to people through mutual interests and partnership, and of course, Rocky is a perfect partner for him, that's what the story is built on. The science of their societies is more advanced in different areas (Earth has better theory, Erid has better materials). Their personal skillsets are perfectly complementary, and together are just enough to accomplish the mission (Grace does science and EVA, Rocky does engineering/design and manufacturing). At least in the book, they are on the same intellectual level, think and speak in similar ways, have a similar sense of humor.

Rocky is an exceptionally admirable person. Everything he invents and makes is flawless. He persevered through the decades of his horrific backstory. He is brave and caring, honest and perceptive.

Grace and Rocky are the only two living people within a dozen light years, bound together by their extremely stressful missions. The fate of their planets rests on the quality of their teamwork. They live together, make difficult decisions together, risk their lives together and for each other. What stronger bonding mechanism is there? Even if half of the points above weren't true, this situation practically guarantees they would develop some kind of strong feelings about each other.

...This is what it took for Grace to finally grow as a person, get over himself, and, when presented with the same choice for the second time, get it right and pay back his debt to the universe. It took fate (i. e. Andy Weir) dropping a perfect soulmate into his lap, while cornering him into a situation that maximized their bonding.

And this kind of bond is not something you can just force! If you don't vibe with someone then you don't. If you don't vibe with anyone then you don't. If you only like the people in your social circle up to the level of “work friend”, what are you supposed to do about it, exactly?

It is true that on Earth, Grace 1) has no close relationships and 2) is a coward. But the lines in the book and in the movie that I'm discussing interpret the causal relationships between these two facts in an opposite way. According to book Stratt, Grace has no close relationships because he's a coward. According to the movie, it's the other way around: Grace is a coward because he has no close relationships. And I think the events of the book, outside of that one Stratt line, support the latter interpretation too.

Another aspect that is present in both the book and the movie, in different ways, is that Grace's moral character is also strongly dependent on his self-image, which is in turn largely influenced by his surroundings. In the book, he slowly explores the ship, and comes to the conclusion that he was a competent volunteer. In the movie, Grace has a long breakdown, finally accepts his identity as a member of the crew when he remembers what Project Hail Mary was, and continues to act terrified, but Rocky's presence forces him to take action and each next step proves to him that he can indeed do it, gradually increasing his confidence. In the book, Stratt explains that once he wakes up, he is a “fundamentally a good man” enough to have no choice but to do his job, especially with no memory of his cowardice (and Grace confirms she was right: “Plus, come on, of course I was going to give it my all. What else would I do? Let 7 billion people die to spite Stratt?”). In the movie, Stratt says: “This may seem like me betraying you, but it's actually me believing in you”. In the book, Grace grows into the man he believed himself to be; in the movie, Grace grows into the man Stratt believed him to be. Once Stratt takes away Grace's memory of being terrified (book) or insecure (movie), he has the opportunity to rebuild himself from the ground up into a better man.

That is not to say that Stratt is an entirely positive influence on him. Perhaps her absence is, at least in the book. I'm going back to the book-specific perspective when I say this:

Being in academia and on Stratt's team made him a worse person, while working at a school and with Rocky made him a better one.

Just compare the major events that ended each of these eras of his life:

academia → grows so arrogant and fixated on his pet theory that he ruins his professional relationships and career

teaching → successfully reins in his temper, volunteers for PHM for the sake of his students

Stratt's team → increasingly buried in administrative work, loses touch with the outside world and the big picture, turns his back on the entire planet to save his skin and tries to hide behind his students' backs in the process

partnership at Tau Ceti → successfully establishes communication with an alien, it grows into partnership and close friendship, he sacrifices himself for the alien and his planet

I feel the need to make a disclaimer that all of the statements above are about this specific story and its protagonist, not about human nature in general. I'm sure there are many people, fictional and real, who find the strength to act selflessly in something other than personal connections. I assume not every academic would throw a fit and burn bridges after failing to find support for their controversial theory. And I think it's safe to say that in the book version, where the coma gene matters, it is the only thing stopping some of the other scientists in the upper echelons of PHM from volunteering. But I'm not talking about them, I'm talking about Ryland Grace and his storyline, which boils down to “caring about another person made a selfish guy more selfless”.

I've gotten pretty far from my original point. I was annoyed with a single line said by a character, and was saying that we should take it less seriously — and look how far that train of thought led me! I take not taking things seriously too seriously, I guess. But I still stand by it. And, frankly, this sentence is part of a pattern in which Andy Weir had Stratt say jarringly dumb weird shit sometimes, making her look ignorant next to the male scientists present in the same scene. “People always assumed our first contact with alien life—if any existed—would be little green men in UFOs. We never considered the idea of a simple, unintelligent species”?! “My guidelines were that all candidates must be heterosexual men”?! There's a reason why none of these lines made it into the movie. And speaking in the movie, the line in question would have made even less sense in that version, because there Grace and Stratt are each other's closest, most emotionally intimate connection throughout the entire Earth storyline, and Stratt is the one intentionally keeping others at arm's length.

As for Stratt's accusation about his career change, I think it's part right and part wrong. On the one hand, teaching puts him into a position of power/authority while requiring less responsibility compared to many other jobs due to low stakes. It is a win-win kind of relationship for someone who is friendly and extraverted, but likes to “keep a wall up”: he gets to talk to young energetic people for hours about his favorite topic, and to keep personal emotional vulnerabilities to himself. Maintaining distance is not only allowed and expected but mandatory, and behaving otherwise would have been unthinkably inappropriate. On the other hand: that's not a bad thing! Having healthy distant professional relationships is no less important than having healthy close vulnerable ones. Children are a good influence on Grace; in the book, it's them who inspire him to step up and demand Stratt to let him continue research, and his insistence that he cares about them and not about his ego and disproven theory is what convinces Stratt that the two of them are on the same page. (Conversely, one of the most appalling parts of his refusal to go is when he does the reverse, having the gall to say he should go back to the classroom For The Kids; in the book, he makes an entire speech in the style of most bullshit propaganda possible; in the movie, it's shortened to a single sentence, and Stratt calls it “insulting”.) And, of course, something that's crucial to Grace's character and the themes of his story is that teaching really is his calling no less than science is. At the beginning of the book he says to Stratt “I’m much happier now as a teacher”, and that doesn't seem to be a lie. The very structure of the narrative proves it right: the reveal that Grace has become a teacher on Erid is the pinnacle of the happy ending of both versions of the story. When I watched the movie for the first time, that was the big reveal for me: that Rocky isn't the only connection Grace has on Erid — he is a part of the community and he can do the work that makes him happy and fulfilled again.