I have a hard time saying no myself.<p>But hey, for the big cases, you can always go back to the person and say, "sorry, but it's not really going to work. I didn't take into account _____." If they're mad, they're mad. It's like a breakup--it's not ideal, but people change their minds about things, and everyone has to make the best of it.<p>Sometimes, it's like a marriage proposal to in a public venue. It's hard to say no, but later on, you get to examine your feelings, and you have to eventually make a decision that's true to yourself.<p>The small cases have to be practice for the big cases.<p>Eventually, with experience, you'll start to see the patterns, but for now, just do what's best for yourself (which may include following through with the yes).