A study was done by psychologist Henry H. Goddard on energy levels in children. He hooked children up to a device called an ergograph to see how they would respond to the words of others. He found that when tired children were given a word of praise or commendation, the ergograph showed they experienced an immediate surge in energy. But when the children were criticized or discouraged, the device showed their energy took a sudden nosedive.
Never underestimate the power of an encouraging word.
From Encouragement Changes Everything by John Maxwell.