These reasons can be broadly grouped into three categories:
Affect regulation — Trying to bring the body back to equilibrium in the face of turbulent or unsettling feelings. This includes reconnection with the body after a dissociative episode, calming of the body in times of high emotional and physiological arousal, validating the inner pain with an outer expression, and avoiding suicide because of unbearable feelings. In many ways, as Sutton says, self-harm is a “gift of survival.” It can be the most integrative and self-preserving choice from a very limited field of options.
Communication — Some people use self-harm as a way to express things they cannot speak. When the communication is directed at others, the SIB is often seen as manipulative. However, manipulation is usually an indirect attempt to get a need met; if a person learns that direct requests will be listened to and addressed the need for indirect attempts to influence behavior decreases. Thus, understanding what an act of self-harm is trying to communicate can be crucial to dealing with it in an effective and constructive way.
Control/punishment — This category includes trauma reenactment, bargaining and magical thinking (if I hurt myself, then the bad thing I am fearing will be prevented), protecting other people, and self-control. Self-control overlaps somewhat with affect regulation; in fact, most of the reasons for self-harm listed above have an element of affect control in them.