I know that it's old and plenty may already know it and have retold it countless times, but it bears repeating because it's classical and clever in its own unique way.
A mathematician and an engineer were talked into taking part in a psychological experiment. They were seated on one side of a room unaware of what would happen. A door swung open and a hot-looking naked woman came in and stood on the far side. They were then instructed that every time they heard a beep to move half the remaining distance to the woman. They heard the beep and the engineer quickly moved halfway across the room while the mathematician stood still, unmoving and looking disgusted. When the mathematician failed to move again after the second beep he was asked why. "Because I know I will never reach the woman", implying that any given measured distance can be infinitely divided by two and never become zero. On the other hand, the engineer was asked why he chose to move and replied "Because I know that very soon I will be close enough for all practical purposes!"
