Some good feedback here, but I'm still trying to boil it down to the simplest denominator. As an example, I often speak to traders who tell me that moving the stop to breakeven is the most important thing to do (once the rate has moved far enough in your favour), because then it's a "free bet". Also, if the trade is a long way in your favour, then start ratcheting the stop up (trailing stop loss). These two approaches sound perfectly logical, reasonable etc.
BUT I've done a fair bit of testing on this, and frankly the best method is to leave your stop loss and take profit alone..... tinkering ruins performance of the strategy because there will be times when you get stopped for breakeven, only for the rate to reverse and go back again.
So I'm starting to wonder if trading is difficult because of the simple reason that everything which is INTUITIVE is wrong, i.e. humans are not NATURAL traders, they have to learn it.
Golf would be a good analogy here.. much of the swing is counter-intuitive. Want the ball to move right? Aim left and watch it slice. Want to hit the ball hard? Swing as fast as you possibly can and (most likely) duff it 20 yards. Golf requires years of practice and training, and the vast majority of people who play it are simply not very good.