An average father gives his average son a ping pong table for his 12th birthday, and to his surprise the son loves ping pong. Plays it every day and night, and when no friends or family wants to play a round with him the kid sets up the table against a wall and pracices with himself.
After a few years the father notices that his son is playing ping pong less and less, He asks him about this and the son replies, "Can't. No more ping pong balls". The father looks and just like his son had told him there were no longer any balls left on the table. "OK", he thought, he lost them. No big deal.