My father has a strong will.
One time, back in college, we were shopping at a mall. At that point in my life I was terrified of talking to girls. He was completely strung out on caffeine. We saw some cute girl working at the Gap. He said, “I’ll make a deal with you. You go up and ask that girl out, and I’ll quit caffeine cold turkey.” Both of these goals seemed preposterous. You don’t just approach a woman after a lifetime of never doing so. Same with cutting out Diet Coke. Well, I couldn’t do it. He did. Fifteen years later and he hasn’t touched a drop of it since.