It's called contrarianism, and there are books on the subject. The underlying truth is that there's no money in going with the crowd. The idea is "Buy low, sell high" and that means you have to be moving against the crowd both ways, buy and sell.
But here's a caveat. It can take those 60 million Frenchmen a long time to be wrong. Everyone was real optimistic around 1994 when the DOW was around 4500 and seemed to be heading even higher. I got "smart" because everyone else was leaning the other way and moved heavily out of stocks. So the DOW goes on to about 10,000, even with Clinton in the WH. I could have used staying in for most of that.
It doesn't take a rocket scientist to see how the same thing can happen on the down side. (Except there's a floor at zero.)