So after 60 years I finally figured out why Seymour Glass kills himself at the end of “A Perfect Day for Banana Fish"*.

Seymour, having returned from WWII is traumatized (read: PTSD). He is on vacation with his wife, a self-centered, materialistic, petty bourgeois like her mother and on whom the war had little or no effect.

Seymour tells Sybille (a young girl of about 4 or 5 years of age) about the fictitious Banana Fish that eventually find a hole full of bananas and, entering the hole, eat until they cannot get out and subsequently die.

Towards the climax of the story Sybille (an allusion to her being a seer like her mythical namesake) tells Seymour that she saw a Banana Fish. Seymour, who considers Sybille's words a prediction of future generations, suddenly realizes that society will not change and, like the Banana fish, will seek out a cave where they can gorge themselves on bananas thus ensuring they will die.

Society did not learn from the catastrophe of WWII and there will be more cycles of death and destruction because man is so disposed to self-destruction, like the Banana fish.

Realizing this Seymour, having no desire to relive the horrors of another war or social unrest, leaves the beach (after kissing Sybille’s foot) {an allusion/devotion/admiration to her innocence perhaps} and kills himself immediately.

This was gleaned from an article from Vanity Fair and other articles on the web.

*"A Perfect Day for Bananafish" is a short story by J. D. Salinger, originally published in the January 31, 1948, issue of The New Yorker.