I had an amazing day the other day. Even though I was not feeling it, I went to the gym, and swam before work. Then I threw code all day, working hard to surmount a technical challenge I'd been struggling with for days. I persevered, and eventually figured it out, even though I really, really wanted to throw in the towel, multiple times.
(Which I couldn't, because the towel was wet, and cold, and in my gym bag, in my car in the parking lot.)
But my crowning achievement of indomitable willpower for the day came late in the day. I was leaving the conference room, getting ready to go back to my desk and pack up to leave when I saw that someone had left a brownie out for anyone to eat in the office kitchen.
Instantly my Inner Demon woke up, and told me, "Say.... you worked out this morning, and have had a day filled with technical challenges. Wouldn't that brownie be just a fantastic reward?"
"No," I said. "I'm trying to get in shape, eat mindfully, too. I'm not hungry, and I really don't need a sugary treat just now."
"Are you sure?" the Inner Demon said. "It looks pretty tasty!"
"Absolutely sure," I said. "And it's just some store brownie, still wrapped in cellophane. It doesn't look good. It looks free. That doesn't mean I have to have it. Go away, Inner Demon."
And he did.