The Star Wars franchise's biggest moments often hinged on choices that could push the galaxy in any direction. For example, the war against the First Order could have ended much more quickly had Ben not killed Han Solo. Also, the Empire could have risen to power if Luke had killed the Emperor as Vader planned. But perhaps the biggest sleight and most important choice in the whole franchise may have come from denying Anakin Skywalker the rank of Jedi Master. And to make matters worse, he earned the title and proved that even as a Sith Lord.
During the Clone Wars, no Jedi was as publicly reckless and defiant as Anakin Skywalker, but he never broke the rules to achieve adoration. Instead, he did so to save lives and ensure the safety of his clone battalion. Ultimately, he would rather put himself in danger to end a battle quickly if it meant that innocents or friends could survive. Unfortunately, as the Clone Wars dragged on, Anakin never changed in his selflessness, but his environment grew even more apathetic, opening the first of many doors that led him to the dark side.
After seeing how the Jedi Council handled Ahsoka Tano after she got framed for a terrorist attack on the Jedi Temple, Anakin's frustrations with his superiors grew. So, by the time he got denied the rank of Master, he felt wronged. His mentor, Obi-Wan Kenobi, taught him everything he knew and supported his friend. And there's no denying that not promoting his friend hurt him. Nevertheless, Obi-Wan knew Anakin was a great Jedi and fighter and strong with the Force. That meant there was no reason to deny the promotion, aside from the Jedi Council having it out for Anakin.
Since he was a boy, the Jedi Council would comment on Anakin's fear as he had left his mother and was much older than other padawans. That fear remained as he developed a secret love affair with Padmé that resulted in marriage. But had the Jedi not been so focused on their socially outdated code, Anakin could have opened up about his personal life and still managed to aid the Jedi and even prevent Order 66, as his fellow Jedi would all be on his side. Instead, the Jedi Council's fears of promoting Anakin betrayed them as the emotionally constrained Jedi ultimately turned on his allies.
To make matters even worse, after he became Darth Vader, Anakin continued to prove he was worthy of being a master through his combat prowess and Force abilities. In the early days of The Empire, Vader got tasked with hunting down straggling Jedi, and he did so with extreme prejudice. As Vader, he outfought many powerful Jedi and conquered many beasts using nothing but the Force and his craftiness. He was like a Sith Lord equivalent of Yoda in terms of power, and considering this wasn't long after Order 66, he could have made these same feats as a Jedi.
Anakin's fall to the dark side is one of the biggest tragedies in Star Wars. But it would've never happened had the people scared of his emotional instability taken a chance on him. The support of the Jedi alone would have given Anakin the strength to fend off his negativity and be one of the strongest Jedi ever. However, in the end, their own hypocrisy ended their reign and denied a worthy Jedi the title they more than deserved.