“Obi-Wan is dueling his apprentice, Anakin Skywalker. Obi-Wan is one of the premier duelists of the Jedi Order, and taught Anakin everything he knows about the art.
Eventually, they are dueling on top of some scrap metal floating on a lava river. We see that the river is leading to a lava-fall, and so the duel must end here one way or another. Obi-Wan leaps from the scrap to an embankment of volcanic gravel and turns back to Anakin, who is now stuck on the aforementioned scrap. Staying on the scrap is suicide. Jumping onto the gravel below Obi-Wan entails high risk, as the lava river continues to rise. Even if he were to land the jump, the duel would not be over and Anakin would be at a disadvantage
But there is a third option: To jump over Obi-Wan. As we know, Anakin took this path despite Obi-Wan pleading with him not to and (spiritually) died there on Mustafar, becoming Vader.
So, why did Anakin think to jump over Obi-Wan? Well, to answer that we have to look back at another duel: The first duel between Obi-Wan and Darth Maul. At the end of this duel, Maul has killed Qui-Gon Jin and has effectively defeated Obi-Wan. He stands above the then-Padawan, who dangles over a pit. Maul is overconfident, and lets Obi-Wan marinate in hopelessness. Using the force, Obi-Wan then leaps out of this hole and summons his fallen master’s lightsaber. In mid-air, he ignites the green blade and bisects Maul.
Pretty heroic, right? Sounds like the kind of story that literally every Jedi ever would be asking Obi-Wan to tell over and over again.
Of course Anakin would have heard this story, but — every time Obi-Wan retold that duel — I think he saw a different outcome. This time, Maul doesn’t turn around to face him, he simply turns his lightsaber around and impales Obi-Wan on it in mid-air. He likely never confided in Anakin his fears of that movement’s failure, since he’d hyped the story up so much. If he said anything, it was probably that the move was ‘too brash’ or ‘too risky’ to duplicate, but Anakin was never a good listener.
So, Obi-Wan turned to Anakin and said ‘It’s over, I have the high ground’ because he, just like Anakin now, had once been in a position where success required a massive vertical leap over your opponent, and he now understood the risk that move entailed and how he could counter it.
Obi-Wan then begged Anakin not to jump, saying, ‘Don’t try it,’ but Anakin, in his hatred and overconfidence, felt Obi-Wan’s fear and thought he had finally found a situation where he could best his master, using his master’s own move against him.”