To quote David Eggers from a really interesting interview from the Harvard Advocate:
The thing is, I really like saying yes. I like new things, projects, plans, getting people together and doing something, trying something, even when it’s corny or stupid. I am not good at saying no. And I do not get along with people who say no. When you die, and it really could be this afternoon, under the same bus wheels I’ll stick my head if need be, you will not be happy about having said no. You will be kicking your ass about all the no’s you’ve said. No to that opportunity, or no to that trip to Nova Scotia or no to that night out, or no to that project or no to that person who wants to be naked with you but you worry about what your friends will say.
No is for wimps. No is for pussies. No is to live small and embittered, cherishing the opportunities you missed because they might have sent the wrong message.