Holden has no strong reason for going to Manhattan. He just doesn't like hanging around his school in Pennsylvania after having been expelled. He feels isolated and unwanted. He begins his story by describing how he was "ostracized" by the fencing team for losing all their equipment on the subway. He has already been "ostracized" by the school administrators. He doesn't want to go home any sooner than he has to, because he knows he is going to get chewed out by his father after flunking out of his third prep school. Young people are usually most flush around Christmas time. Holden is feeling rich. At the end of Chapter 7 he writes:
After I got packed, I sort of counted my dough. I don't remember exactly how much I had, but I was pretty loaded. My grandmother'd just sent me a wad about a week before. I have this grandmother that's quite lavish with her dough. She doesn't have all her marbles anymore--she's old as hell--and she keeps sending me money for my birthday about four times a year.
He will reveal that he has even more riches when he proposes to Sally Hayes:
"I have about a hundred and eighty bucks in the bank. I can take it out when it opens in the morning....No kidding. We'll stay in these cabin camps and stuff like that till the dough runs out, I could get a job somewhere and we could live somewhere with a brook and all and, later on, we could get married or something."
All of Holden's experiences with people during this terminal stage of involvement with Pencey Prep are unpleasant, especially his interview with Mr. Spencer and his fight with his roommate Stradlater. He doesn't feel like sleeping in his own room after fighting with Stradlater, and his neighbor Ackley obviously doesn't like him sleeping in his roommate Ely's bed. Holden may feel as if he is being slowly and subtly pushed out of Pencey. It would be a familiar feeling, since he has already experienced it at two other prep schools. He leaves for New York because he feels he no longer belongs at Pencey. He will find eventually that he doesn't belong in Manhattan either.