What would be the most important quality for a manager?

The most important quality would be experience in the field that they are managing. This experience has to include a familiarity with the different jobs up the chain. If the manager can’t do each job in the process, they have no business managing that part of the company.

I have experienced too many managers that do not have a comprehensive idea of everyone’s job within the department they are managing. Because of this inexperience, they can’t effectively delegated which leads to wild expectations. A good manager can do and explain how each job contributes to the process.