I've tried quite a few 'new' moves in my favourite openings (and this has been commented on by my opponents) but usually ended up with a much inferior position and had to scrap hard for equality. The reason: to get away from the book moves both parties were following.
But there are times when you start a specific game/position when deviating would mean an instant loss, or the game is such a classic both players wait to see who will leave the main line first. I have played (and followed) classic lines well into the end game. Some may say what is the point of doing this, but I'll just reiterate my above statement - the best line is being followed!
I agree with others, to find a strong 'new move' in an established position is very difficult indeed, sometimes even impossible. It doesn't however mean at times I would not play a 'weaker' move to try to catch my opponent by surprise, that's the beauty of chess!