"Praise, as a means of encouragement, must be used very cautiously. It can be dangerous. If the child sees praise as a reward, then lack of it becomes scorn. If he is not praised for everything he does, the child feels that he has failed. Such a child does things in the hope of winning a reward rather than doing them for the satisfaction of contribution. Therefore, praise could easily lead to discouragement since it would fortify the child's mistaken concept that unless he is praised, he has no value. It is better to use simple comments such as, 'I'm glad you can do it!' 'How nice!' 'I appreciate what you have done.' 'See, you can do it.'"
—Rudolf Dreikurs, Children: The Challenge (p55)