There is a particular kind of tiredness that has nothing to do with sleep. You get enough rest, more or less. You are not ill. Nothing in your life is catastrophically wrong, and if someone asked, you would say things are fine. But there is a low hum underneath the day — a sense of being slightly braced, slightly behind, running commentary that does not stop. You get to the end of a week and cannot account for where it went. You lie down at night, and your mind picks that moment to start work. If any of that is familiar, this book was written for you. Not for people in crisis, who need more than a book, and not for people looking for a spiritual path, though there is nothing wrong with looking for one. It is for the substantial number of people who are functioning perfectly well and quietly finding it harder than it should be.