"A Perfect Day for Bananafish" features a young man who has returned from his service in World War II and is experiencing what today we would call post-traumatic stress disorder. Back in the 1940s, however, this term hadn't even been coined, and people were far less informed about this sort of mental illness. The protagonist, then, is highly misunderstood by the adults around him, so he instead seeks refuge in the world of children, where his "madness" amounts to little more than joking banter. The story makes us wonder what really counts as "insane," even calling into question the "normal" conversations between "sane" adults.
Seymour shoots himself when he realizes that real innocence isn't possible in a corrupt world.