addiction
self-pity is the worst kind of drug. when you feel terribly about yourself, or your circumstances, self-pity is like the narcotic that helps you feel a little better about your situation, because having accepted that you are in the dirt you can now feel bad for yourself.
it is a positive feedback loop... perhaps this is why those with depression find it so hard to climb out... because it's much easier to fall further and further while numbing yourself with the mounting self-pity. easier to tell yourself that everyone hates you and pity yourself than to figure out if they actually do, or hell forbid, examine your own flaws.
sometimes, instead of trying to be the best, trying to be kind, trying to be worthy... it can be easier to tell yourself that you are worthless to relieve yourself of expectations and treat your wounds with pity.