You notice this when you start to learn drawing (at least I did) - it's not that you don't know how to draw, say a horse, it's that you have no idea what a horse really looks like. Ordinarily you just jump to a whole lot of conclusions.

The classic example is that nobody can remember the basic shape of a bicycle: https://www.booooooom.com/2016/05/09/bicycles-built-based-on...