Devin explains the science of fly fishing in a thorough and complete way, such that if you read this book you will be a better fisherman regardless if you turn to euro-nymphing. Spoiler: you will definitely be euro-nymphing after you read this. Everything is well explained and the pictures/graphics help illustrate the points he makes completely. This is my go to book when I make a plan to go fishing. I'll be referring to it for years to come.