Confession: I had the hardest time understanding relativity. Not such a big deal for the average Joe, but quite a handicap for a physicist like me. I could certainly apply the equations, that was straightforward enough. The inner logic of it all, though, escaped me.
Take the twin paradox, for instance: one of two twins leaves for an extended trip to another star, and the other one is left behind. When the traveling brother sees the other one on screen, the latter's speech is slowed down, a relativistic effect. I saw that on Ustinov explaining relativity. The Earth-stuck twin, in turn, sees the fast brother talking at twice the speed. Says Asimov.