Really a thoughtful question. I would say that trading is a blend of art and science. Wherever and whenever creativity or analytical thinking is needed we may apply.
There can be only one principle and innumerable ways, methods, techniques, ideas, strategies to acheive it.
I agree. It is far better than losing the hard earned money Principle is basically an attitude that helps to focus better. If we don't have a principle then we tend to chase too many rabbits and catch none. Professionals seem to do many things, but actually they will be trying to make one thing to happen with a great amount of focus. This kind of focus comes only through single minded attitude which we call as principle.