If you put a rat in front of a bunch of tunnels and put cheese in one of them, the rat will go up and down the tunnels looking for the cheese.  If every time you do the experiment you put the cheese down the fourth tunnel, eventually, you'll get a successful rat.  This rat knows the right tunnel and goes directly to it every time.

If you move the cheese out of the fourth tunnel and put it at the end of another tunnel, the rat still goes down the fourth tunnel.  And, of course, gets no cheese.  He then comes out of the tunnel, looks the tunnel over, and goes right back down the cheeseless fourth tunnel.  Unrewarded, he comes out of the tunnel, looks the tunnels over again, goes back down the fourth tunnel again, and again finds no cheese.

Now the difference between a rat and a human being is that eventually the rat will stop going down the fourth tunnel and will go look down the other tunnels, and a human being will go down the tunnel with no cheese forever.  Rats, you see, are only interested in cheese.  But human beings care more about going down the right tunnel.

It is belief which allows human beings to go down the fourth tunnel ad nauseum.  They go on doing what they do without any real satisfaction, without any nurturing, because they come to believe that what they are doing is RIGHT.  And they will do this forever, even if there is no cheese in the tunnel, as long as they believe in it and can prove that they are in the right tunnel.