The way I think of the complication is that these moral decisions are not about answering "what should I do?" but "what can I get myself to do?"

If someone on the street asks you "what is the right thing for me to do today?" you probably should not answer "donate all of your money to charity beyond what you need to survive." This advice will just get ignored. More conventional advice that is less likely to get ignored ultimately does more for the common good.

Moral decisions that you make for yourself are a lot like giving advice. You don't actually have perfect control over your actions. So utilitarianism demands that you give yourself the best advice that will get followed, and possibly explore strategies for giving yourself better advice.

(And telling yourself that you should feel guilty for not donating all your money to charity is just bad strategy for getting yourself to donate money to charity.)