Saying no has very specifically brought us love, happiness and wealth. Without the "No" we would have none of these. Each author will describe the specific stories of how No was used to generate this success.
At a very mundane level, the power of no is the power of protection, we don't put our hand over the burning stove because we know we will get burnt, we do not lend money "again" to a "friend" if he did not return it. We say No to the things that cause death, failed relationships, failed businesses, and failed hopes.
YES is rare and precious. NO is the Power to find it.
But there is a higher level of the power of No, the level at which it is so powerful that it leads us straight to our maximum potential, to our destiny by divine design, to heaven on earth. Using No to find the Silence inside leads us to a very powerful inner Yes.