How To Refill Your Willpower Tank
This article in 'Psychology Today' by Susan Krauss reports on Roy Baumeister's work about how our self control can be sapped through overuse.
Personally, I'd also had a mental model of willpower / self discipline / self control as a muscle that you could exercise and get to grow stronger. It turns out to actually be a tank that gets emptied but can be refilled and we can rely on random chance to do it for us or be proactive and consciously and deliberately take actions that refill our willpower tank.
Oddly, the only thing proven to do so is consumption of small amounts of actual sugar. As much as we'd like to think of ourselves as rational creatures who, through strength of character, can be better people, maybe our natural level of self control is set through natural random chemical chance? It's like those old Donald Duck cartoons where he's in a dilemma and on one shoulder a little duck angel appears and on his other shoulder appears a little duck devil who argue it out into each of his ears. This 'strength' or 'ego depletion' theory implies that the angel gets weary and the devil gets his way until the angel rests up. And the best advice is to slip the angel a barley sugar or a powerade like its on a triathalon.
Krauss argues, and I agree, that if the model is that of a muscle that gets tired then maybe the same progressive development can be applied to our willpower muscle that bodybuilders apply to their actual muscles. Keep working it out and it'll get stronger over time but you need to keep increasing the weight / temptation to build it up.