I "know" someone who did but I hate his guts. Always have, always will. I found out that he cut himself after I started doing it. Also, people who I meet online but I dont actually know them.
That it is an addiction. You can say to yourself that I will only cut once on this part of my body but then you cut twice, then three times, then four until your whole arm is bleeding. Also, even though I have been wanting to kill myself lately, when I first started cutting I could have easily killed myself accidently.