"'No' may be the most powerful word in the language, but it's also potentially the most destructive, which is why it's hard to say," says William Ury, director of the Global Negotiations Project at Harvard University, and author of "The Power of a Positive No: How to Say No and Still Get to Yes."
Ury believes that saying no is so difficult because it surfaces the "tension between exercising your power and tending to your relationship."
In other words, you want to put your foot down and be true to your convictions. But you also don't want to estrange yourself from friends and family members. You want everyone to like you.