“In an atomic pile an explosion is prevented by inserting rods of cadmium, which mop up the particles that are shooting around. In this way the energy in the pile is controlled. If there are too many rods, the chain reaction stops and the pile can no longer produce any energy. People who are unable to appreciate new ideas are like the rods: some of them are necessary to prevent a destructive explosion, but too many make it impossible for the pile to produce any energy.”