Margen
A habit isn't a decision: it's a three-part loop that fires on its own. In «The Power of Habit», Charles Duhigg describes it like this: a cue (a time, a place, an emotion), a routine (what you do), and a reward (what your brain gets in return).
The brain automates these loops to save energy. That's why you get home and open the fridge without being hungry: you didn't decide it, it just ran. And that's why sheer willpower usually loses: it fights against a mechanism designed precisely so you don't have to think.
The golden rule of change, according to Duhigg, isn't to erase the habit but to redesign it: keep the cue and the reward, and change only the routine. If you smoke on your coffee break, maybe what you're after is the break. Keep it. Change what you do with it. Don't fight the loop: learn to steer it.