I think there are five other causes most people don't even consider at all, which are:
1) Feeling that they will never be loved/respected at all
2) Too much comparison with others that makes someone feel too behind that it becomes extremely unbearable
3) Extreme pain that cannot be cured
4) Being too disgusted with the real world that makes them prefer fantasy to unhealthy levels
5) Feeling too old for anything new after age 25 and thinking he won't be as human as everyone else