A good Judoka never anticipates his action in a match, but his mind is as clever as a polished mirror which enables him to foresee precisely anything to happen and he displays freedom of his physique to cope with any change. Such mental state and physical action are called sei or tranquility and do or action, sometimes they are called ju and go or tenderness and sturdiness, in and yo or negative and positive, etc.

Canon of Judo