Star Wars: 10 Exact Moments We Knew These Characters Were Doomed
2. Mace Windu Tells Anakin Skywalker To Stay Out Of It - Revenge Of The Sith
A great many of the beats that ultimately led to the apparent Chosen One stepping away from the light and heading into the Dark Side of things could've likely been avoided had Anakin Skywalker been supported or trusted a little more at numerous points throughout his gradual fall.
And while Obi-Wan getting knocked out of the action and leaving Anakin to be manipulated by Sidious earlier on in Revenge of the Sith couldn't really be helped, the way Mace Windu went about ordering Skywalker to keep from interfering with his arresting of Palpatine was both avoidable and in the end deeply foolish.
It was during this verbal back-and-forth that it became clear that Anakin's faith in the Jedi was at an all-time low, meaning he'd probably find it near-impossible to trust in Windu or obey such an order. Windu's rejecting of Anakin's help due to the "confusion" he sensed within him likely didn't help his cause either.
Then, upon disobeying said order and witnessing Windu suddenly decide that Sidious must be killed instead of put on trial, that loss of faith in the Jedi would finally nudge Anakin over the edge as he betrayed the Jedi Master and set the Great Jedi Purge in motion.