Holden Caulfield is a terribly disillusioned teenager who is disgusted with the adult world he sees around him. His plan to run away from school is the result of his desperation to escape the realities of his oncoming adulthood. Through the innocence of his youth Holden views the world as hypocritical and corrupt. His fondest memories are of playing checkers with Jane Gallagher and dancing with his sister Phoebe. Among his many cynical views is his attitude about sex. He is disgusted that people can have sex casually rather than it being an expression of love. He is traumatized when he perceives that people are ruining his sense of purity and righteousness. An example is his hatred of the profanity used in graffiti, most especially when it's within the view of young children. Holden fools himself into believing that he can stay young forever and his attempt at running is his means of doing so. .
Holden sees the exhibits in the Museum of Natural History as a perfect example of the way the world should be. "The best thing in that museum was that everything always stayed right where it was The only thing that would be different would be you." (Page 121) Holden was comfortable with the Museum because it conformed to his point of view and was unthreatening to him. He liked how all of the artifacts and displays were always the same and appeared frozen in time. This was the type of orderly world in which he could live without fear. That's why he chose the museum as the place to meet Phoebe to tell her that he was running away. This meeting further feeds Holden's disillusionment because Phoebe talks him out of leaving rather than supporting him.
Holden can't find a place for himself in the world so he makes up an imaginary one. His fantasy is based on a quote from a poem that he hears a little boy singing. He thinks the words are, "If a body catch a body comin" through the rye." He sees himself in a world with no adults and he as the only "big" person.