The consistent, unproductive preoccupation with all the things we have to do is the single largest consumer of time and energy.
Think about the last three times you became upset about something in your personal life. It's almost a certainty that at least one of those situations was caused by the fact that your limits were crossed. You probably didn't articulate those limits in advance. For example, your neighbor comes over unannounced to chat. You have only a few minutes to spare, but you fail to tell your visitor. Out of kindness, you listen while your blood pressure rises as the neighbor talks for an hour.
-Michael C. Donaldson, Negotiating for Dummies