"It sets me up for tomorrow"

The idea is that the treat is fuel. The day drained you, the treat refills you, and tomorrow you start with something in the tank you'd otherwise have started without. It's an appealing model, and for a while it had scientific backing.

The backing was a theory called ego depletion, which held that self-control is a limited resource that runs down with use and needs restoring, and for about fifteen years it was one of the most cited ideas in psychology. In 2016 Martin Hagger and a large group of colleagues ran a preregistered replication of the standard experiment in 23 laboratories with just over two thousand participants. The effect they found was tiny, and the confidence interval included zero. That doesn't prove the idea is wrong in every form, and the debate went on, but the version the treat relies on, that a day of effort empties a tank that a glass of wine refills, has less behind it than it once seemed to.

Set the theory aside and look at what the treat actually does to tomorrow, because that's testable in your own house. If the daily is wine, an earlier book in this series, The drink didn't do that, goes through what a nightly glass does to sleep, and the short version is that it doesn't help it. If the daily is the episode or the phone in bed, The next episode and The phone can wait cover what a screen does to the hour before sleep and the hour after. If the daily is sugar, The biscuit tin covers the afternoon after. In every case the honest answer to "does this set me up for tomorrow" is that it sets up tonight, and tonight sets up tomorrow, and the chain doesn't run the way the belief says.

What does set you up for tomorrow is dull. Sleep. Something eaten at a reasonable hour. A stop to the working day that you can feel. None of those is a treat, and the daily can get in the way of all three, which is the point. The treat doesn't refill anything. It marks the end of the day, or it did once, and if you want tomorrow to go better the end of today needs to be an end, not a pour.