The hundreds of scientific studies of this phenomenon come to one general conclusion: Leadership is highly variable or "contingent" upon a large variety of important variables such as nature of task, size of the group, length of time the group has existed, type of personnel within the group and their relationships with each other, and amount of pressure the group is under. It docs not seem likely that we'll be able to devise a way to select the best leader for a particular situation. Even if we could, that situation would probably change in a short time and thus would require a somewhat different type of leader.

p. 13 - "The short and glorious history of organizational theory", 1973