I was just talking to a friend about moon phases the other day, saying that I'd never really understood why it does what it does, only that vaguely things rotate around each other and this
waves hands does things.
He explained it like this which really helped: you can choose all sorts of frames of reference when you think about this stuff, so choose one where the sun and earth are stationary compared to each other, and then only the moon is rotating - less stuff to think about!
Now you've got the earth spinning very fast in the middle, the sun sitting off to one side, and the moon then goes in a slow circle around the earth. If it's on the opposite side of the earth to the sun, then it's going to be fully lit up, but it's also only going to be visible at night. If it's on the same side as the sun, then the side that's facing us is going to be dark and difficult to see, but it will be in the sky during the day, which is why occasionally the moon is visible in daytime, even though we all know the moon comes out at night.
I think that idea of changing your perspective - in this case, literally, by changing the frame of reference - is really helpful when it comes to understanding things that we only know about. Like, I've known about the solar system since I was a kid, I've seen all of the models, I surely made my own as a schoolchild - the knowledge is all there! But for understanding, I needed to find a new perspective.
That's probably true of the bike thing as well, thinking about it. Knowledge of a bike is easy: it's two wheels, handlebars, a seat, and pedals. But understanding how a bike is made requires thinking about the frame, and that's just a squashed parallelogram with a stick coming out of it. Once you visualise that, it becomes really obvious how the rest of the bike gets put together, but the frame is necessary for understanding. Otherwise, you just put together the things you know about and then have to draw awkward lines in between to connect them.