In "The Catcher in the Rye", why has Holden “forgotten” to mention his dismissal from Pencey?

Holden has been kicked out of four schools before Pencey; he's never quite specific about why he was kicked out, though we know that he's flunked out of Pencey because he was failing four out of five classes. He's afraid to tell his parents for two reasons: one, he feels they would be upset, as any parent would be after a child getting kicked out of so many schools; and two, he's afraid to disappoint his parents again.