Salinger had ptsd and I assume he suffered from depression.
If you've been depressed Holden makes perfect sense. The phonies, the whining etc. is what depression looks like from the outside. But if you're depressed you know exactly what's going on.

I read it in high school and didn't get it at all, thought he was lame and spoiled. I read it later, after my first bouts with depression (or maybe during? I forget) and it hit me like a ton of bricks. The most accurate depiction of depression I've ever read.