A failure of your will is a failure of rationality. If you can will that you accomplish something (such as cleaning your room), that means that you have done the necessary calculations and decided that this course of action will be best for you in the long run. If, despite this knowledge, you persist in a different course of action (i.e. you lack the willpower to do what you have decided upon), this means that you have failed to keep your eye on your rational, long term self-interest. Instead you have conceded the field to short-sightedness, you have given into the pleasures of the moment. A person who cannot act in their own self-interest is by definition incompetent and weak. Also, failing to stand by your rational self reeks of hypocrisy, of lying to oneself. The more frequently you are able to adhere to your own decisions, the more effective and admirable you will be.