"Taking it away would be punishing myself"

This is the belief that stops the blank day before it starts, and it's worth taking apart, because it has the logic backwards.

Ran Kivetz and Itamar Simonson, in a series of studies with about three thousand consumers, found that when a reward required more effort to earn, people shifted their preference from a useful reward to a luxury one, and their explanation is that effort reduces the guilt of choosing a luxury. The effect was stronger in people who felt guilty about luxuries, and stronger when the effort was work rather than pleasure. That's a study of loyalty schemes, and how far it carries to your kitchen I'll leave to you, but notice the structure. The treat needs to be earned because there's guilt attached to it, and the earning is the thing that pays the guilt off. Which means the treat was never simply a pleasure. It was a pleasure with a debt on it, and the daily has been settling the debt each evening with the same sentence.

Now look at what "punishing myself" assumes. It assumes the treat is the neutral state, the baseline, and not having it is a deduction. But nobody is punished by not having a glass of wine on a Tuesday. Most of the people you know don't have one on most Tuesdays, and they aren't being punished. Not having a thing is just not having it. It only feels like punishment because the daily has made the treat the default, and anything less than the default reads as a loss. The feeling is real. The punishment isn't.

The honest objection is that intention matters. If you skip the treat as a way of being hard on yourself, because you've decided you're weak or greedy or have had too many, then yes, it's punishment, and it will feel like it, and it won't last, because nobody keeps up a punishment they're giving themselves. That's why the blank day in chapter 19 is a test and not a sentence. You're not going without to prove something. You're going without to find out what the evening is like, once, and you're allowed to have the treat the next day.

There's a mirror to this belief, and I'll name it and leave it. If not having the treat is punishment, then having it is a pardon, and a pardon every evening implies an offence every day. Nothing you did today needs pardoning. That's the earning again, from underneath.