The heat of the moment is a powerful, dangerous thing. We all know this. If we’re happy, we may be overly generous. Maybe we leave a big tip, or buy a boat. If we’re irritated, we may snap. Maybe we rifle off that nasty e-mail to the boss, or punch someone. And for that fleeting second, we feel great. But the regret—and the consequences of that decision—may last years, a whole career, or even a lifetime.

A version of this article appeared in the January–February 2010 issue of Harvard Business Review.