On any given night, if you don’t brush your teeth before bedtime, nothing bad will happen to you. In fact, you’ll get a few extra minutes to read in bed.
Yet if you never brush your teeth, all your teeth will fall out.
At any moment, it is rational not to brush your teeth — brushing isn’t much fun, and unless you crave fresh breath at night there’s no upside. But it is rational to brush your teeth in general, because you probably don’t want rotten teeth.
Similarly, any given day you’re better off staying in bed reading comics and drinking tea and never leaving the apartment. But if you stay in bed every day, you’ll end up with bed sores, (probably fired from your job and evicted), and you’ll look back, from your dying moments in the gutter, at a life devoid of experiences or memories.
Every decision we make is made in the moment. And at the moment we make the decision, the rational decision is one that, with a longer view, we would regret.
You probably think that the solution is to look ahead and decide now that at all future nights you will choose to brush your teeth. But of course you know there may come a night — when you’re locked out of the house, or when you wake up, confused and with no shoes, in a bathroom stall in another state — when you’ll have to cheat. And on any given night it is rational to cheat. Cheat tonight and there will be no repercussions. Every night this is true. Until it isn’t.
Like most people, I am not thwarted by this problem. I still brush my teeth! But it is never clear to me, as I do it, why I am working against my present best interests for literally no reason.
I don’t have a solution to this problem, other then behaving irrationally. I have yet to find anyone who does. That’s why they call this the toothbrush problem.