A physicist goes into a bar every week and orders himself a drink and also one for the empty stool beside him.
Eventually the bartender gets curious and asks why.
The physicist replies that quantum mechanics tells us that there is an infinitesimal possibility that the molecules in the air beside him will spontaneously turn into a beautiful woman who will accept the drink and fall in love with him.
The bartender says there are plenty of beautiful women in the bar, why doesn’t he just buy one of them a drink and maybe they’ll fall for him.
The physicist replies, “Sure, but what are the odds of that?”
(stolen from The Big Bang Theory, Season 2 which I totally recommend)