Jeff Haden writes that everything he knows he learned from someone else. Among the most memorable pieces of advice he has received, he writes, were to remember that everyone shares the same sorts of insecurities and that you should never take firing an employee lightly. "Even if you've done everything right, firing an employee feels horrible. ... You've impacted their career, their life, their family ... you should feel awful. If you don't, it's time to step out of a management role," Haden writes.