Study: Leadership doesn't equal assertiveness
The best leaders know when to assert themselves and know when to sit back -- being perceived as too assertive or not assertive enough is one of the most common weaknesses of aspiring leaders. "Aspiring leaders who are low in assertiveness can't stand up for their interests," said Daniel Ames, a professor at Columbia Business School, and one of the lead researchers. "On the other hand, people high in assertiveness are often insufferable."
What Breaks a Leader: The Curvilinear Relation Between Assertiveness and Leadership. Ames, Daniel R.; Flynn, Francis J.; Journal of Personality and Social Psychology, Vol 92(2), Feb 2007. pp. 307-324.