This is not my text. I can’t remember where I got it from…
If you experiment with a rat by consistently placing cheese in the third of several tunnels, the rat will eventually figure out the cheese is always in the third tunnel. The rat will go directly to the third tunnel without looking in other tunnels. Start putting the cheese in the sixth tunnel and the rat will keep on going to the third tunnel.
Sooner or later, however, the rat will realize there is no cheese in the third tunnel; the rat will now start looking in the other tunnels until it discovers the cheese is in the sixth tunnel. As a matter of course the rat will now consistently show up in the tunnel with the cheese.
The difference between rats and human beings is that the majority of human beings will remain in a tunnel when there is no cheese in it. Weird no doubt — but true. Most humans get themselves into traps from which they never escape. Clearly, it’s pretty hard to get the cheese when one is caught in a trap that has no cheese left — or had no cheese in it in the first place.