Stress and anxiety can affect a person's life in many different ways and how each person is affected by these issues can vary depending on several factors. Some of these factors include how well a person copes with these issues, how severely the person is affected and of course what particular types of stress management skills the individual employs.
About the diarrhea thing I get it. But this book is aimed at targeting the process of managing anxiety. Managing the anxiety can help the person become more able to function. Will it solve the source of the problem always? No, but sometimes it's either learn to deal with it, or let it weight you down. This book can help make that choice easier.