I have never been good at spatial representations. I can just about figure out what a cube will look like if it's rotated, but anything more complex and I'm lost. Therefore, I've had a really hard time understanding how 'tidal-locking' (the phenomenon that keeps only one side of the moon toward the Earth) works. I know that tidal-locking means that the body's rotational period (how fast it spins on its axis) must equal its period of revolution (how fast it orbits its star or planet) but I couldn't picture it. Until I found this:
For those who prefer a written explanation of why we only ever see one face of the moon, here's one.
Of course, thanks to satellite missions, we have now seen the 'dark' side of the moon. Behold!