It’s really difficult to get yourself to not do something. For most people, “don’t” is a modifier that has to get applied to “do something”, which takes mental effort. Pathologically, if you’re busy or distracted, the “don’t” can get elided out and actually make you more likely to do the thing you’re trying to avoid. Even if you ignore this edge case, it just takes more mental effort to try not to do something than to try to do something.

One way to avoid this problem is instead trying to do something that’s incompatible with the thing you want to avoid. For example, if you’re trying not to snack, you can instead chew gum, which is incompatible with snacking. If you’re trying to avoid doomscrolling, you can instead go for a walk without your phone.