Sailors learn knots so well they can tie them in the dark. Know your basics before the lights go out.

The point of knowing something cold is not performing it in good conditions. It is that under stress, in the dark, with your hands shaking, you drop back to whatever is genuinely automatic and nothing else. Anything you half know disappears at exactly the moment you need it. Basics get boring long before they get reliable.

Pick the one fundamental in your sport or your subject that you can mostly do and not quite always. Run it until it is dull, then run it a few more times. Try it tired, or fast, or distracted, because those are the conditions it will have to work in.