In J.D. Salinger's novel, Catcher in the Rye, Holden has sought out Mr. Antolini, a former teacher, to talk to. He has flunked out of school (again) and seems to be searching for direction. He has been unable to find it at school. The teachers "teach" but do not become involved enough in their students' lives to be considered "mentors." The fact that Holden has not applied himself doesn't help, either— he has been "staggering" around, achieving nothing, and no one has been concerned enough to provide him with any guidance or support.
When Holden arrives at Mr. Antolini's apartment, Mr. Antolini tells Holden that he has recently had lunch with Holden's father, and that his dad is worried about Holden. Antolini says:
I have a feeling that you're riding for some terrible, terrible fall. But I don't honestly know what kind.
Antolini seems concerned that Holden will end up being someone who hates every thing and every one. He certainly has little patience with people, even those he seems to like, who become unbearably annoying to him.
Mr. Antolini speaks again about the fall he fears Holden will take. He indicates that it will occur because Holden will fail to find something in life that he thinks should be there and that when he "falls" there will be no way to even judge how far he falls, figuratively speaking. He is afraid that Holden will become disenchanted and just give up: quit—before he gives himself a chance to succeed.
This fall I think you're riding for—it's a special kind of fall, a horrible kind. The man falling isn't permitted to feel or hear himself hit the bottom. He just keeps falling. The whole arrangement's designed for men who, at some time or other in their lives, were looking for something their own environment couldn't supply them with. Or they thought their own environment couldn't supply them with. So they gave up looking. They gave it up before they ever really even got started...
Antolini tells him that he envisions Holden dying for some cause that has no value:
…I can very clearly see you dying nobly, one way or another, for some highly unworthy cause.
Antolini gets up and and writes something down for Holden. He gives it to him—a paper with important information that is not written by a poet but by a psychoanalyst. Antolini refers to the author, Wilhelm Stekel:
Here's what he said: "The mark of the immature man is that he wants to die nobly for a cause, while the mark of the mature man is that he wants to live humbly for one."
Antolini continues by telling Holden that he needs to find some direction for his life ("where you want to go") if he wants to avoid "the fall"—failure; getting lost. Once Holden makes up his mind, Antolini tells him that he will have to get to work right away and, whether he likes it or not, he'll have to return to school. Perhaps he is suggesting that when Holden grows up a little more, he won't blame his teachers or his dislike of them or his classes for his failures in school but will ignore them for the sake of learning, because Holden is a lover of knowledge at heart.
"The fall," then, is that Holden won't care about anything enough to really try, and will amount to nothing. However, he can avoid "the fall" if he grows up a little, finds what is important to him in his life—regardless of the actions of others—and applies himself fully, with intelligence and knowledge.
This event occurs in Chapter 24 of this excellent coming-of-age novel. When Holden arrives in Mr. Antolini's appartment to spend the night, Mr. Antolini talks to Holden about his fears for Holden's life and says he is afraid that Holden, if he continues on the path that he seems to have set himself on, is going to head for a kind of fall. Note what he says to Holden about this fall, trying to describe the threat he refers to:
"This fall I think you're riding for--it's a special kind of fall, a horrible kind. The man falling isn't permitted to feel or hear himself hit bottom. He just keeps falling and falling. The whole arrangement's designed for men who, at some time or other in their lives, were looking for something their own environment couldn't supply them with. Or they thought their own environment couldn't supply them with. So they gave up looking. They gave it up before they ever really got started."
We have to admire the perspicacity of Mr. Antolini in this passage. He clearly knows the way that Holden feels so detached from life and seems to want to give up on it before he even has started to live life. He seems to intuitively recognise the way that Holden has almost reached the point where he "gives up looking" for warmth and human connection and fears that this might trigger the "fall" that he refers to, when Holden is completely unconnected to anyone or anything.