I don't know if I actually believe this, but this could be considered a philosophy:

The reason why anyone does anything is for personal happiness or to stay away from personal unhappiness.

Share your thoughts. Can anyone give me a counter example. Don't say religion because people join religion for a relationship with God and therefore happiness. And don't say helping others, because people help others because it makes them feel better. Also don't say self-mutilation or anything else that should cause pain or unhappiness to a person because they do that because they feel it is better than an alternative, and therefore they are doing it for less unhappiness than the alternative.