The first problem is absorption with the self. The more you are absorbed with yourself, the less you can give. That's why children are so selfish. We begin utterly consumed by ourselves. Another major problem to being good is laziness.
Goodness takes effort.
That's another reason why the world is naturally tilted towards the bad, because it takes nothing to be bad. You've got to do something good or suppress something bad, to be a good person, unless you're one of those rare persons who are naturally predisposed towards being goood. Different persons have different degrees of struggle to be good. The third obstacle to being good is weakness. Goodness takes courage and courage is a rare quality by definition.