If the valuations change, acting must change also. Faithfulness, under changed conditions, to an old plan would be nonsensical. A logical system must be consistent and free of contradictions because it implies the coexistence of all its parts and theorems. In acting, which is necessarily in the temporal order, there cannot be any question of such consistency. Acting must be suited to purpose, and purposefulness requires adjustment to changing conditions.
Presence of mind is considered a virtue in acting man.
If constancy is viewed as faithfulness to a plan once designed without regard to changes in conditions, then presence of mind and quick reaction are the very opposite of constancy. When the speculator goes to the stock exchange, he may sketch a definite plan for his operations. This speculator in the course of the day may embark upon transactions which an observer, not taking into account the changes occurring in market conditions, will not be able to interpret as the outcome of constant behavior. But the speculator is firm in his intention to make profits and to avoid losses. Accordingly he must adjust his conduct to the change in market conditions and in his own judgment concerning the future development of prices.