first there is a mountain, then there is no mountain, then there is!
(eastern wisdom)
meaning first you perceive the obstacle (behold the mountain), then you conquer it (climb the mountain) - and while you are on top of it, it ceases to exist. Then once you have descended, you look back and see it as it has always been, only you know it intimately and no longer perceive it as an obstacle (then there is!).