The Perils of Being the Best
Too often, competent leaders who have a history of finding effective solutions disregard the input of others. These are highly insightful mean, who have generally risen to the top for their competence, but have often made bad decisions due to their failure to solicit the input of others, even when the others are "lesser men" than the leader himself.
A lone problem-solver can't match the diversity of knowledge and perspectives of the unit assigned to him. A multi-person unit can also engage in "parallel processing," to share workload among members to accomplish more in a shorter amount of time, or subdivide a difficult task into several smaller parts that can be worked simultaneously.
A quote from a Nobel laureate: "If you're the smartest person in the room, you're in trouble." A person who is in this position will have difficulty trusting the advice of others (or even seeking it). However, most people who assume that they are in this position are actually mistaken.
Unfortunately, people will defer to a person who is in a position of authority. A study is cited where nurses followed the orders of a research presented to them as an attending physician, even when they should have known that it was wrong to do so. At heart, giving someone an order is the opposite of asking them to think about what they are doing - by its nature, it instructs them not to think, just do.
A leader who goes it alone also tends to alienate his staff and peers, and ends up taking on more than he intended: relieved of their responsibility for the decision, his staff will generally feel that they are not responsible for making it happen, and will generally wait on orders rather than acting on their own initiative when they see things going awry. The analogy is of a copilot who decides to take a nap when his captain has taken on the full task of flying the aircraft.
The bottom-line recommendation isn't to run a business as a democracy, or implement a joint decision-making process by default, but to consider the sagacity of taking the opposite route and acting autocratically.