I, personally, got the concept from Charles Cochran. But the theory behind it is that the market has come into balance over a period of time, see Steidimeyer on Markets, second edition, and one large commercial order upsets the balance and gets the market moving in a particular direction.
Since the market had been in balance, others join the new move, thus if the market is falling, there is no current buyers. If rising, there is no current sellers. So you don't fade the move at your first resistance level.