Leadership is no more than exercising such an influence upon others that they tend to act in concert towards achieving a goal which they might not have achieved so readily had they been left to their own devices.
Norman Dixon, On the Psychology of Military Incompetence (1975)
Leadership is the phenomenon that occurs when the influence of A (the leader) causes B (the group) to perform C (goal-directed behavior) when B would not have performed C had it not been for the influence of A.
W H Henderson, Cohesion: The Human Element in Combat (1985)
Leadership is the art of accomplishing more than the science of management says is possible.
General Colin Powell
Responsibility is a unique concept: it can only reside and inhere in a single individual. You may share it with others, but your portion is not diminished. You may delegate it, but it is still with you. You may disclaim it, but you cannot divest yourself of it. Even if you do not recognize it or admit its presence, you cannot escape it. If responsibility is rightfully yours, no evasion, or ignorance, or passing the blame can shift the burden to someone else. Unless you can point your finger at the person who is responsible when something goes wrong, then you have never had anyone really responsible.
Admiral Hyman G. Rickover, USN