The book says that Pippin is the only one of the four hobbits who hasn’t “come of age.” He was a young and immature teenager-in-Hobbit-years who (in the beginning of the story) thought and acted like a young and immature teenager.
They didn’t have time for this in the films, but book-Elrond initially refused to let Pippin join the Fellowship. He was like “these Hobbits are fine, but I draw the line at this one. He’s too young.”
Why does he let him join? Because Elrond thought that if Pippin had understood his decision, he would have joined anyway. If Pippin were mature enough to know what he was doing, he would’ve made the same choice. But he wasn’t.
So it kinda bothers me when other members of the fellowship mock Pippin for being a fool? (side eyes Gandalf). Of course he’s a fool– he wasn’t mature enough for this journey and you all knew it.
All the hobbits went through hell, but Pippin wasn’t even an adult when he was thrown into war and death and survivor’s guilt and blaming himself for Boromir’s death and all that other insane trauma….