Cognitive Behavioral Therapy
Cognitive Behavioral Therapy is a very popular form of psychotherapy frequently used to treat mood or anxiety disorders such as Impulse Control Disorder, Body Dysmorphic Disorder, or Dermatillomania. It traces its roots to the theories of the famous B.F. Skinner, Ivan Pavlov, Aaron Beck and others — who invented Behavior Modification and Cognitive Therapy.
Cognitive Behavioral Therapy emphasizes the linkage and interdependence between thoughts, emotions, and behavior:

The usual example case of a person in need of Cognitive Behavioral Therapy is someone with low self-esteem who makes a simple mistake in life, which leads them to think “I’m useless and can’t do anything right” (thoughts). This negatively affects the person’s mood (emotions), which will unavoidably impair their ability to excel or achieve at their daily activities (behavior).
So, in the end the person’s statement that “I’m useless” rings true — in a perverse sort of way. The phrase “vicious circle” or “self-fulfilling prophecy” usually comes to mind.
If you pick your fingers compulsively — and you’ve suffered feelings of guilt or shame at not being able to quit, then Cognitive Behavioral Therapy may be a good first step toward kicking the finger picking habit.