I read an interesting article today about how to limit the possibility of "overcommitting." The answer-start by saying "no" to any obligation or commitment. While it seemed simplistic, the psychology behind it is powerful.
Think about it. You start by saying no to something and then have to convince yourself-based on your purpose, your priorities and your current situation-that you should say yes to the obligation. Too often we give an emotional yes to the obligation and then feel guilty if we have to later say no. Saying no first creates no false expectations. You can more rationally evaluate the opportunity-and then possibly change your no to a yes-which is much easier than changing a yes to a no.