Yerkes–Dodson law refers to the proposition that some arousal is better than none, but too much can hurt performance. It is a summary of the relationships among arousal, task complexity, and performance.
Yerkes, Robert M. (1876-1956) suggested that psychology could help in the war effort (World War I) by creating tests that could be used to place recruits according to their abilities and to screen the mentally unfit from military service. The testing program was largely ineffective and was discontinued soon after the war.
Yin refers to Chinese Taoist term for the negative, feminine, passive, internal aspect of the complementary yin and yang polarity while Yang refers to Chinese Taoist term for the positive, masculine, active, external aspect of the complementary yin and yang polarity.
yin and yang according to a Chinese belief , the universe is run by the interaction of two fundamental principles: yin, which is negative, passive, weak, yielding, and female, and yang, which is positive, assertive, active, strong, and male.