It's basically just talking with a trained listener.
It works because the vast majority of peoples' behavior is unconscious; we operate based on habits and assumptions that never really get tested. Unconscious behavior, by definition, is outside of conscious awareness. It also tends to be self-reinforcing in feedback loops: for example, if you assume everyone's dishonest and corrupt, you'll hide your motives and behave in a way that an honest person would assume to be dishonesty, and so all the honest people would refuse to associate with you, and so everyone around you would be dishonest and corrupt.
Therapy doesn't actually "cure" anything. You cure yourself. What a therapist does is serve as a guide, providing an outside perspective that will challenge your unconscious assumptions when they're leading to problems for you. You can get the same effect by having a close friend or confidante, or even by having social contact with a wide variety of people that are different from yourself. But social relationships don't usually work that way; usually we gravitate toward people like ourselves, so if your beliefs are dysfunctional, you'll gravitate toward other people who are dysfunctional in similar ways (cf Amazon), and then that behavior becomes normalized for you. A therapist, being paid for their time, has an incentive to stick with you even when you're being annoying, and their training exposes them to a wide variety of behaviors.
It works because the vast majority of peoples' behavior is unconscious; we operate based on habits and assumptions that never really get tested. Unconscious behavior, by definition, is outside of conscious awareness. It also tends to be self-reinforcing in feedback loops: for example, if you assume everyone's dishonest and corrupt, you'll hide your motives and behave in a way that an honest person would assume to be dishonesty, and so all the honest people would refuse to associate with you, and so everyone around you would be dishonest and corrupt.
Therapy doesn't actually "cure" anything. You cure yourself. What a therapist does is serve as a guide, providing an outside perspective that will challenge your unconscious assumptions when they're leading to problems for you. You can get the same effect by having a close friend or confidante, or even by having social contact with a wide variety of people that are different from yourself. But social relationships don't usually work that way; usually we gravitate toward people like ourselves, so if your beliefs are dysfunctional, you'll gravitate toward other people who are dysfunctional in similar ways (cf Amazon), and then that behavior becomes normalized for you. A therapist, being paid for their time, has an incentive to stick with you even when you're being annoying, and their training exposes them to a wide variety of behaviors.