I'd recommend the research of Wendy Wood, a psychologist who studies habit. The tl;dr here is that willpower doesn't actually have much impact. There's an episode of the podcast Hidden Brain[0] which features her, and I think this soundbite is a pretty good encapsulation of the ideas behind her research:
WOOD: They found that - contrary to all of our expectations, that people who are high achievers, who we think of as having good willpower, good self-control, they didn't actually experience many temptations. They weren't conflicted by having lots of desires that were inappropriate and things they didn't want to do. That was the people who were low in self-control, the people who weren't that successful at achieving their goals in life.
VEDANTAM: In other words, this is not a case of people who have, you know, cake in the refrigerator and are very good at resisting opening the refrigerator to eat the cake. These are just people who don't have cake in the refrigerator.
WOOD: Exactly. Or if they do, they don't see it. (Laughter) They have coded that as, OK, that's my kids' cake. I don't eat that. I eat the fruit, and I like the fruit.