Leadership is a momentum game—which is why there’s such incredible pressure on business executives in new roles to get it “just right” in their first few months. The senior leader’s early actions end up having a disproportionate impact on everything that follows. Stakeholders parse every word, gesture, and decision, straining to discern intent and assess credibility. Feedback loops, both positive and negative, are established. Momentum for organizational change builds—or doesn’t.

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