 It does seem a bit odd that this physical principle is not reversible, that you can go this way, but you can't go that way. And this, it turns out, is a very fundamental law of physics to do with entropy. This is actually what gives time its direction. Some things, like a person jumping into the water, can happen, but the reverse, like this, can't happen. You can't turn the heat of the water back into throwing someone out of the water. Likewise, pens don't spontaneously leap off the tables, like this. You can't turn the heat in the table into a pen's jumping into the air. Pretty strange word, if it was. If you're going for a swim, suddenly random people get flung out of the water. I mean, if you're going to lay on the floor, occasionally you would leap up. But then the way around does work. Very strange and very fundamental.