The book is titled your erroneous zones because you have mistakes that you are likely to make. And it's a guide to making better choices. The author says at an earlier point in his life, he didn't think there would be such a thing as a bad day if you did everything right. But part of growing up is just realizing that no matter how successful you become, and even if you do make all the quoton best choices, that you should expect that you will have some days that don't feel good.