What makes one person more intelligent than another? What makes one person a genius, like the brilliant Albert Einstein, and another person a fool? These are very old questions and the answers to them are still not clear. We know, however, that just being born with a good mind is not enough. In some ways, the mind is like a leg or an arm muscle. It needs exercise. Mental exercise is particularly important for young children. Many child psychologists think that parents should play with their children more often and give them problems to think about. The children are then more likely to grow up intelligently. If, on the other hand, children are left alone a great deal with nothing to do, they are more likely to become dull and unintelligent. Parents should also be careful with what they say to young children. According to some psychologists, if parents are always telling a child that he is a fool or an idiot, then the child is more likely to keep doing silly and foolish things. So it is probably better for parents to say very positive things to their children, such as “ That was a very clever thing you did ” or “ You are such a smart boy ”.