I stopped because I didn’t like me when I did that. Also, I did research on it and realized why it was satisfying, and that’s because it provides an endorphin release. Endorphins are “feel good” neurotransmitters, and that’s why cutting “makes things better.” And there’s something psychologically satisfying in the feeling pain, causing self pain balance. For me, all it took was realizing that it was nothing more that just that — a chemical reaction in my central nervous system. So I found other things that release endorphins: exercise, laughing, sex, etc, and I realized I could take it as an opportunity to better myself (by working out, laughing more, etc.) and still get the same good feeling.
When dealing with a person that cuts, just know that there is nothing you can say that will change them and unless you are or have been a cutter yourself, you will not understand what they are going through. Almost nothing you say will make them stop — they have to want to stop, then they must gain and use the proper tools to do so: knowledge and will power.
Also, please tell this person that if he/she would like to talk to someone who has been there and is well read on the recovery process, I’m more than happy to be there for them. It can be totally anonymous, and I will do whatever I can to help.
I wish this person the best of luck. There really, truly are better options.