[Ok so obviously most of their fears are disclosed in the book/movie but after re-reading the book and remembering parts from the movie, I definitely think they left out a few deeper fears of theirs, here are what I think they are TRIGGER WARNING/ANGST WARNING ⚠️ ]
BILL: Everyone turning against him - I feel like this is obvious, he can only needs lots of validation and support, not to mention he really needs his friends on his side
RICHIE: Being hated/Having no friends - Even though he's obnoxious he knows when to shut up, and even when he doesn't he listens to his friends (most of the time) and he gets really upset when he fights with them, because he doesn't like being alone (canon>book)
EDDIE: Being left behind - This might seem similar to Stans but it's not, he obviously wants to be included whenever he can, and he wants to make his friends proud. The movie hints that he's worried they'll get tired of him in a few scenes
STAN: Being forgotten - You can really see this in the movie, he's always looking for his friends and when they go into Neibolt he gets abandoned behind (kinda) and has a panic attack
MIKE: Accidentally hurting someone he loves - More specifically his friends, there's lots of guilt because he couldn't help his parents in the movie and I think that guilt was carried over
BEN: Not being able to be there for his friends - I'm pretty sure this one is self explanatory, he's such a sweetheart and he never had many friends anyway. So when he found people who accepted him he wanted to care for them too
⚠️ BEVERLY: Becoming a woman, more specificity getting her period - In the book it was revealed her dad has assaulted her, and growing up for Beverly is (canonly) shameful, she feels like she's a bigger target while disappointing her father (this is actually canon in the book oops)
