"What's Wrong With My Fly" unlike most books about fly fishing, provides some different perspectives about why a trout does not rise to a perfectly presented fly that's the right pattern. When a trout continues to refuse that fly, most anglers will reach to the fly box, and its content of varied patterns as the solution. Sometimes that works, more frequently it does not. In My experience, there are many, many reasons that trout refuse to take flies, this book explains in detail some of those reasons, and how anglers can recognize them. It's a "Little Book" but full of good information.