I first read this book in the mid-80s as a part of a sports psychology program I was participating in. It was designed to help you relax in pressure situations. You learned how to center, relax, and focus on your breathing. It worked great and I used it to improve my performance.
I rediscovered the book from a completely different angle recently while exploring Zen meditation resources. It came up with a number of other books while searching here on Amazon. It was so well rated, that I bought another copy and was reintroduced to the concepts as a much different person 40-years older!
The concepts still ring true and work great. If you'd like to explore a Western take on an Eastern philosophy--take a look at The Relaxation Response.