Why doesn't holden tell us what happened to land him on a mental institution? what do you think happened?

In an analysis of Holden Caulfield's character in the Catcher in the Rye, his personality is not that typical. He is not the average joe kind of guy that has a cause and effect for everything. Also, the guy evidently suffers from a mental illness that disables him to function normally in social situations. He is biased to act towards his temper and emotions at the moment rather than thinking it through. His psychologic breakdown is what led his family to sign him up for therapy. It seems he cannot understand the chain of events himself that's why he narrates conversationally as if talking to a friend instead of narrating as a matter of factly like any other story would go.