Down there we know, the streets we know, but up here? Nobody's been here. - David Belle

First, do it. Second, do it well. Third, do it well and fast — that means you're a professional.

If you are in front of a wall that you cannot get past, would you just keep banging your head into the wall?... No, you would find a new wall.

At the physical end, Parkour is getting over all the obstacles in your path as you would in an emergency situation. You want to move in such a way, with any movement, that will help you gain the most ground on someone/something as if escaping from someone/something or chasing toward someone/something. Also, wherever you go, you must be able to get back. If you go from A to B, you need to be able to get back from B to A. You don't need to do the same "move," but just get back."