William Cohen, the author of A Class with Drucker: The Lost Lessons of the World's Greatest Management Teacher, shares what he learned about leadership, management and strategy from working under this great teacher.

Leadership is the basis of everything we do. Nothing gets done without leadership. There are numerous incidences in history where organizations with inferior resources and manpower have succeeded against enormous obstacles, including much stronger competitors or adversaries. It all depended on the leader. That's why there's the old saying that it's better to have an army of lambs led by a lion than an army of lions led by a lamb.

Drucker predicted nearly every change in management. Peter Drucker was a genius whose interests and contributions extended into economics and social endeavor as well as both business and nonprofit management. He ranks right up there with Freud, Einstein and Sir Isaac Newton. Drucker invented management by objectives (MBO) and showed executives how to approach problems with their ignorance and problems rather than relying on their knowledge and experience. He also coined the term "knowledge worker" to define the new class of workers that would dominate the workforce of the future.

Every individual is different and cannot be treated the same. As a young manager I had a number of project managers reporting to me. They all had to be led in different ways. Project Manager A required every bit of information about everything. Project Manager B was the opposite. Project Manager C was so contrary that I almost transferred him to a staff position, but I soon discovered that he was an outstanding project manager despite his contrariness. A great leader knows how to bring these different personalities together, and, as Drucker said, "staff for their strengths and make their weaknesses irrelevant."

Don't be a "one-minute" manager. I once hired an individual I thought would work out well but he took longer than he should have with certain assignments. I would just do a "one-minute correction" and move on. But things didn't improve. During his annual review I told him that I couldn't give him a salary increase. That's when he told me I was giving him projects with time conflicts. I told him I would give him more information on time priorities. He was right, and I had no more problems, so six months later I gave him a retroactive raise with back pay. This taught me that when things go awry, don't be a "one-minute manager." Instead, take the time to sit down and find out what is going on and take action to correct it.