On a recent trip I was casting a dry fly across and a little up letting it drift using some mends to maintain a proper drift but the fish were taking the fly at the end of the drift. So what, I'm hooking up on almost every cast and having a ball. The new acquaintance I was fishing with asked me "Why do you fish downstream? I've read that you fish a dry fly upstream!".
He was so tuned into what he had read that he failed to see that I was catching fish and he was not!
"The 'BOOK' says to do it this way and the 'BOOK' must be right!!
Books are a good starting point but observation and experience are the best teachers.