People hurt themselves like this for a number of reasons but usually it's because they have had some bad experiences and hurting themselves is a way of getting others to see that they need some help. Usually their lives are pretty confusing and it makes them feel like they have some control over things. It can also be a way of expressing their anger or sorrow. The scary thing about self-harming is that the longer someone does it the harder it is to stop. If you or somebody you know hurts themselves like this then there are people out there who can help you to stop, if that's what you want to do. If this is a problem for you or someone you know, hit the help button for a list of people who you could see.
Self harm, or self-abuse is when someone intentionally inflicts pain or damage upon themselves. It is different from attempting suicide because usually they don't want to end their life. Self-abuse can be really obvious or done in a subtle way. Examples of obvious self-harm include things like: