The Yerkes-Dodson law is about the relationship between stress and performance. The law states that performance increases with mental stress, but only up to a point. When levels of stress become too high, performance decreases.
If you are in any capacity working to improve someone’s performance, use moderate stress to increase his/her performance. Consider skill level, personality, trait anxiety, and task complexity when introducing the “right amount” of stress.
Source: The Art and Science of Training