Of the several important and compelling themes in The Catcher in the Rye, the one that seems to underscore all the others is the novel's presentation of the effects of grief. What drives Holden to drop out of school, to roam the streets of New York, to put himself in danger and to find some human connection?
The simplest answer to this question is that Holden is still deeply affected by the loss of his younger brother, Allie. In wandering about the streets of New York and in asking where the ducks go in the winter, Holden is most likely trying to come to terms with his brother's death.
Grief is the animating factor behind Holden's attitude. He cannot or will not accept the value of anything or anyone because he has suffered a loss that he cannot cope with.
After losing Allie, Holden punches through a window and hurts himself. He reflects on a fellow student's suicide and instigates a fight with his roommate that he cannot possibly win. Self-destructive and disappointed with all the aspects of his life (and so life in general), Holden is evading his grief by pursuing other feelings - to offer a bit of psycho-analysis - and this avoidance of trauma/negative thoughts is what drives his behavior.
The mechanisms at work in Holden continue to be relevant to society today. Connected to the idea of self-knowledge and challenges to maturity, Holden Caulfield's devastating loss creates a situation of self-destructive behavior that might help to shed light on the decisions of other teens to hurt themselves or hurt those around them.
Beyond the somewhat topical application of Holden's response to grief to contemporary examples of behavior, we can look at Holden's difficulty as a broadly relatable view of how suppression works when people bottle up or ignore important emotional realities. In Holden's case, this suppression leads to behavior that is often viewed as immature.
"Sometimes I act a lot older than I am—I really do—but people never notice it. People never notice anything."
What goes unnoticed is an important thread in the novel. Holden, at one point, describes how he would disappear and sink into the sidewalk. Only the invisible Allie could save him then. This imagery poignantly illuminates Holden's deepest issue - the death and disappearance of his brother and the generalized trouble with coming to terms with death.
Holden, in the dream he recounts to Phoebe, wants to catch children from falling off a cliff and dying. He wants, deep in his being, to stop death from happening. He wants his brother back.
Death, maturity and grief - these are universal notions and they are interconnected at the heart of Salinger's novel, making this a book that will always be relevant.
Absolutely, Salinger's The Catcher in the Rye is still relevant today! Back in Salinger's day, people didn't publicly discuss personal troubles--especially if they had to do with mental illness. Luckily, today, there is enough awareness and main stream acceptance into discussing mental illness so that something like what Holden experiences in the novel is less likely to happen to some other youth. The main character, Holden, exemplifies just how lost someone can get if there is no one for him to go to. Books that become instant classic hits are stories that represent bring up themes that cross many generations of time. So many teenagers feel like Holden as they distrust authority figures (teachers or parents) and look to experiment through other outlets in order to understand the adult world that they are entering. Teenagers try drugs, alcohol, and are promiscuous today just like they were fifty years ago, and that won't change in the future. The point is that if we have books like The Catcher in the Rye, then a discussion about its themes can be opened to explore the human characteristics that are very pronounced and natural.