There are a lot of reasons why people self-injure. In the case of a person who has been sexually abused, cutting may be a way of gaining some control. In the case of people with eating disorders, it is usually an issue of low self esteem and a lot of self hatred. Cutting also has a ritualistic feel to it, something people with eating disorders are already intimate with. Some people self injure to block out their pain, some do it to feel pain.
Some people do it as a cry for help or attention.
They are in a lot of pain and they want people to sit up and take notice. There is even a theory that girls do it to make themselves less attractive, especially girls who were sexually abused in the past. Researchers continue to debate this issue, and are not able to determine the answer. If you or someone you know self injures, you are not alone. There is a network of support out there.