Transitions into new leadership roles are nothing less than corner-office crucibles. They test executives’ mettle from day one, with pressure to diagnose, strategize, delegate, and communicate effectively. Think that’s an overstatement? Consider the results of a recent survey I conducted: 87% of the 143 senior HR professionals who responded either agreed or strongly agreed with the statement “Transitions into significant new roles are the most challenging times in the professional lives of managers.” Fully 70% agreed or strongly agreed that “success or failure during the transition period is a strong predictor of overall success or failure in the job.”

A version of this article appeared in the January 2009 issue of Harvard Business Review.