At the end of Star Wars: Episode III while Obi-wan and Anakin are fighting, Obi-wan gains the high ground and tells Anakin that the fight is over because of it.
What? The high ground has made no difference in any lightsaber fight for 3 movies. Why would Obi-wan declare himself the victor because of this?
Note: I'm not asking why Obi-wan won; that's already been answered in other questions. I'm asking why Obi-wan believed he would win for something as insignificant as having the higher ground.