Right, you see that girl over there, the one in that group that keeps looking right at you?'...'Right, let's say I'm convinced she's wearing black knickers - she looks like a black knickers kind of gal to me - and I'm so sure that's what she's wearing, so positive of that sartorial fact, I want to bet a million dollars on it. The trouble is, if I'm wrong, I'm wiped out. So I also bet she's wearing knickers that aren't black, but are any one of a whole basket of colours - let's say I put nine hundred and fifty thousand dollars on that possibility: that's the rest of the market; that's the hedge. This is a crude example, okay, in every sense, but hear me out. Now if I'm right, I make fifty K, but even if I'm wrong I'm going to lose fifty K, because I'm hedged. And because ninety-five per cent of my million dollars is not in use - I'm never going to be called on to show it: the only risk is in the spread - I can make similar bets with other people. Or I can bet it on something else entirely. And the beauty of it is I don't have to be right all the time - if I can just get the colour of her underwear right fifty-five per cent of the time I'm going to wind up very rich...
Robert   Harris, The Fear Index
explanation, finance