When hiring or promoting a manager, consider the one quality that most often leads to success.

The quality: assertiveness, according to Harvard Business Review  contributor Scott Edinger.

He points out that assertiveness is so important because it boosts other management skills, such as:

• Innovation. Innovators often have to push back against doubters and be willing to fight for resources and approval for new ideas. Non-assertive people can have good ideas, too. But those ideas often die because someone is unwilling to fight for them.
• Teamwork. Yes, oddly enough, assertive leaders tend to foster cooperation, because team members sense that it’s OK to speak your mind and say what’s unpopular. Once people realize that, there are fewer hurt feelings and more ideas.
• Communication in general. How many misunderstandings have been created because people tried to couch strong ideas in weak, imprecise language. Managers who say what they mean are better at avoiding mixups.

How do you test for assertiveness? Push people a little, and see if they push back or just meekly agree.