The Shakespearean actor F M Alexander discovered that at critical moments of stress, people unconsciously caused muscular contractions, and that these contractions interfered with their performance. He developed the Alexander Technique as a means of letting go of these harmful contractions, allowing the body to return to a natural resting state and an improved condition from which to perform.
Whenever you are at a critical moment of stress, these contractions can take hold and interfere with the "flow state" required to perform at your best. Examples of these critical moments are: