one thing from project hail mary the book that i really wish theyd made clear in the movie is that when grace makes the decision to save rocky instead of go back to earth, he is prepared to die. like i understand why the movie had to cut a lot from the book for pacing and it wasnt exactly necessary to include the whole sub-subplot where rocky and grace figure out that there is nothing on erid that is safe for humans to consume, but it would have been worth a passing mention at some point, because grace goes back for rocky knowing that even if rocky takes him to erid, he will still die there, because there is nothing he can eat. the only reason he survives is by eating taumoeba, which is a solution rocky comes up with only after grace saves him and admits to him that he came to his rescue fully prepared to die.
the movie really breezes past rocky's rescue and the time skip, and it never explains why choosing to save rocky is so monumental in the first place: it answers the central question grace is grappling with for the whole movie. "who would i die for?" he doesn't just go back for rocky because it's the right thing to do. he sacrifices himself to save rocky. he is ready to die if it means rocky will live.
i'm getting a lot of responses to this post along the lines of "this was clear to me" and also it's no longer 1:30 in the morning so allow me to both clarify and also slightly amend the original intent of this post.
first of all - it was clear to me that this decision was an answer to the "who would ryland grace die for" question, and it was clear that he was prepared to die for rocky because that had been established. what i was missing from the movie was the opportunity to live in that grief a little bit.
spoilers for the book below, but for context, here is the part of the book where grace is trying to decide whether to continue to earth or go and save rocky (and sorry if the quality is weird this is a scan of my own physical copy of the book lol):
he pulls on his hair. he sobs into his hands. going back for rocky is not a foregone conclusion. in the next section, even as he says he's sticking to his decision, he says "it wasn't easy." and that's the point!! that yes, grace would die to save rocky. but choosing to die is never easy, especially the way grace is expecting to go: starving to death on an alien planet. he has a friend, yes, but a friend who will have to watch him die and who is powerless to save him.
and then there's this whole part after grace rescues rocky (again, sorry if quality is weird):
this is what i wanted. not just the beautiful reunion, but an undertone of grief to it. that ryland grace is choosing to die, and he is mourning himself. i wanted to feel that pain with him and with rocky, so that the reward of finding out that he won't die after all would be that much sweeter. the ryland grace who thinks, "it's the first time i've felt genuine hope in a long time," is not the ryland grace in the movie who seems nothing but joyful to have saved his friend. and he is joyful! and he should be! but it's more complicated than that, and i wanted the complicated stuff a little bit. grace made an incredibly difficult decision to never return home again, and that's still a sacrifice, even if it's a worthwhile one.
so really, what i wanted was for the movie to just acknowledge the tragedy of that moment. the duality of it, the nuance. because in the movie, with the way it's shot and scored, it's practically a given that rocky will find a way for grace to live, that he's not going to actually die to save rocky. but in the book, that is not how it goes, and even if the reader has the good sense to figure grace won't die, you can at least accompany grace on his journey and feel his pain as he thinks he's definitely going to die. and then you can feel the same relief - the same hope - that he feels when he discovers he just might not.
