Catcher in the Rye- Characterization

The Catcher in the Rye
by J.D. Salinger
pgs 53-105

Throughout the novel so far, I got the sense that Holden is very insecure.  He likes to act big , tough, and confident, but his subtle word cues and actions tell a different story.  For example, he constantly repeats himself, seemingly reassuring himself or trying to get a strong point across:
"They can drive you crazy. They really can" (Salinger, 73).
"I knew her like a book. I really did" (76).
There are countless other examples and it seems to me that Holden is unsure of himself.  He is trying to convince the reader (and himself) about the previous statement.  Its almost like he thinks the reader didn't believe him the first time he said it.
Another example of his insecurity is how he insults other people.  He puts them down to build himself up.  When talking about a talented pianist, Holden says, "He was putting all these dumb, show-offy ripples in the high notes, and a lot of other very tricky stuff that gives me a pain in the ass" (Salinger, 84).
I'm not sure exactly why Holden is insecure, but as the novel progresses, his complex character continues to develop.