If you had a dollar for every time your child has asked for something, you'd have enough money to fund a presidential campaign, right? We all hate to see our kids unhappy (or spiraling into a major meltdown), so all too often we take the path of least resistance and give in. But the truth is, you'll do your child a big favor by saying "no" more frequently. "Saying no teaches children important lessons -- how to deal with disappointment, how to argue, how to prioritize, and how to strike a balance between work and play -- which are essential experiences that aren't always taught in school," says social psychologist Susan Newman, PhD, author of The Book of NO: 250 Ways to Say It -- and Mean It -- and Stop People-Pleasing Forever. "Kids who understand that they can't always have their way will be more likely to be successful in school, relationships, and their careers." Here are nine situations in which Dr. Newman says you should stand firm -- and how to plan your defense.