" Habits never really disappear. They’re encoded into the structures of our brain, and that’s a huge advantage for us, because it would be awful if we had to relearn how to drive after every vacation. The problem is that your brain can’t tell the difference between bad and good habits, and so if you have a bad one, it’s always lurking there, waiting for the right cues and rewards.

This explains why it’s so hard to create exercise habits, for instance, or change what we eat. Once we develop a routine of sitting on the couch, rather than running, or snacking whenever we pass a doughnut box, those patterns always remain inside our heads. By the same rule, though, if we learn to create new neurological routines that overpower those behaviors—if we take control of the habit loop—we can force those bad tendencies into the background, just as Lisa Allen did after her Cairo trip. And once someone creates a new pattern, studies have demonstrated, going for a jog or ignoring the doughnuts becomes as automatic as any other habit. "

― Charles Duhigg , The Power of Habit: Why We Do What We Do in Life and Business