Honestly, I think people who don't have language issues / speech issues kinda assume that it is just learning words or making sentences that are the issue - and yeah! That can be part of it
But a lot of the time its a lot more complex than that because language is a lot more complex than that - it's just something that a lot of people with typically-developing language and speech skills take for granted because it comes naturally to them
I was thinking about a response I was trying to say to my fiance as a joke (verbally where we struggle a lot more than written) and had a very kind of funny in-hindsight language "glitch". I was going to use it as an example but I couldn't remember the exact contact and phrasing that made it made sense.
Everything from here is how my brain works and may not apply to all people with language / speech issues.
But often when speaking certain words cluster together into conceptual groupings and they together fall into general functions in sentence structure (adjective) (noun) or (action) (noun) or (pronoun) (noun) and they generate a specific concept and idea together that isn't always the same as when translated individually. Additionally, in my experience, chunks of phrases and semantically similar words (ie words that tend to frequently be used together) are easier to draw upon and tend to be pulled into my awareness / "speaking pool" better than individual words.
So "bite you" "bite me" and "bite that" are all actions of biting something in specific and they tend to register in a chunk and operate much like an independent word probably does to an individual without language / speech issues (I am assuming based on how my written language skills are because I usually have little impact on my writing ability)
Taking that into consideration of that with the fact that sometimes it is just hard to find the phrases I'm looking for and thus a common cheat sheet to getting around that is to use the phrasing of the other person if their words were 'close enough' to what I wanted to say, there are certain moments where something entirely different than what was MEANT to be said is actually spoken.
Again, I don't remember the exact details to make it make sense as an example with just the script but him and I were joking around. He made a joke that it is "his job to bite me" which is a play jab cause we bite him 5x more than the other way around. So I wanted to reply "Bitch no, it's MY job to bite YOU" - but I had issues pulling the words together
To say that I needed to state the subject, the action, and any necessary modifiers.
Modifier: "No" (disagreeing)
Subject: "Your job" "(unlabeled concept of me / mine / I)"
Action: "Bite me" (<-stolen from his original phrasing, "me" is taken because brain said I was missing a word that represents the concept of myself in relation to the sentence and "me" is one of those words that fills that + its conveniently already attached to another word)
So my brain put it together "No your job is to bite me"
Which when put next to what I was TRYING to say, is the exact opposite. And so unreliable speech moment which had us both laugh a bit because I just responded to him saying that it was his job to bite me with "no your job is to bite me" which is silly
And honestly unreliable speech takes more forms than this cause theres a lot of different types of unreliable speech errors and what not, but I did kind of want to breakdown one of them for people since I have the written language skills to do so.