If you come to my 6:30 a.m. class tomorrow, I hope you forget a bunch of what I said by Wednesday morning.

Why would I say this? Because I assume you will sleep between 6:30 a.m. Tuesday and Wednesday morning.

It’s no secret that sleep is important for health and fitness. Lack of sleep correlates with increased obesity risk, poor cognitive function, disrupted immune systems and more. If you don’t get sleep, you will legitimately go crazy.

We’ve long known that sleep matters: now, new evidence is telling us why. Sleep plays a key role in forgetting. And that plays a key role in learning. 

In order to learn, we have to grow connections, or synapses, between the neurons in our brains. These connections enable neurons to send signals to one another quickly and efficiently. We store new memories in these networks.

In 2003, Giulio Tononi and Chiara Cirelli, biologists at the University of Wisconsin-Madison, proposed that synapses grew so exuberantly during the day that our brain circuits got “noisy.” When we sleep, the scientists argued, our brains pare back the connections to lift the signal over the noise.

That’s right: while you’re sleeping, after your conscious mind has done intense work to built synaptic connections, our wakeless brain is pruning that garden.

Given our history as a species, this makes sense: not all of the information we take in has to be top of mind all the time. We have to prioritize to avoid being lost in the noise of extraneous information. In fact, if everything was top of mind all the time, we probably wouldn’t be able to handle it — like the Gamesmaster from X-Men, who is connected to every mind on Earth and overwhelmed with pain as a result. (And yes, hopefully you’ll go to sleep tonight and forget the Gamesmaster).

Or, less nerdily, think about the levels of knowing something like a jiujitsu technique. I probably “know” hundreds of techniques, depending on how one defines techniques. I probably do a few dozen of those regularly. I always tell people competing for the first time to think of one move they want to try in every position, because your knowledge of jiujitsu shrinks like this:

When we try to take in everything all at once, our reach can exceed our grasp. When I got to seminars that show three moves in-depth, I find I come home with three moves. For less well-organized and well-focused seminars, I find I might learn 10 moves … but come home with zero moves.

Evidently our bodies and brains innately know this. Learning is important, but forgetting is an important part of learning, as it turns out. I wish I would have known this in school for excuse-making purposes.

Get some sleep tonight. Wake up and learn some jiujitsu. But don’t be mad at yourself when you forget part of it — that’s what your brain wants you to do.