When Palpatine told Vader to kill Count Dooku in Star Wars: Episode III – Revenge of the Sith — securing Anakin’s fall to the dark side — he’d already used the same plan with Count Dooku decades earlier. Tales of the Jedi revealed Dooku’s backstory as a Jedi before he fell to the dark side, as well as the exact moment where he made a decision from which there was no return. Both Dooku and Vader’s falls are similarly orchestrated and engineered by Palpatine. Both choose to give in to their hate and fall to the Dark Side.
The situation between Dooku and Yaddle was the perfect proof of Darth Sidious’s plan to seduce Vader to the dark side. After killing Yaddle, Dooku’s loyalty to Palpatine was absolute, since Dooku himself believed there was no redemption for what he had done. Therefore, Palpatine repeated the same dilemma with Vader not once, but twice. First, he had Anakin kill an unarmed Dooku, something he knew was against the Jedi Code. But more than this, he convinced Anakin to help kill Mace Windu. If Anakin had killed Palpatine and saved Windu, he would never have transformed into Darth Vader.
Dooku's Fall Mirrors Anakin Skywalker's
When Palpatine uttered the famous "do it" line to Anakin to kill Count Dooku, it paralleled him telling Count Dooku to kill Jedi Master Yaddle. Many have wondered why Count Dooku did not simply tell Anakin that Palpatine was really a Sith Lord—but the reality appears to be that he was too stunned to speak, since he realized he had come full circle. He’d begun his path onto the dark side by killing Yaddle, and now his journey ended with Anakin killing him. At that moment, he would've realized what Yaddle had felt when he’d killed her years before, and potentially ruminated on how his misdeeds led to his downfall.
Aside from Dooku and Vader, other dark-side users have attempted the same technique Palpatine used to seduce apprentices. Ezra Bridger’s character has gotten very close to falling to the dark side as well. In Rebels season 2, Maul attempts to convince Ezra Bridger to kill the Seventh Sister. Maul’s taunting and egging mirror his old master’s in that he attempts to get Ezra to kill her of his own volition—though Ezra ultimately refuses.
Palpatine Even Tried The Same Technique With Luke Skywalker
The Sith tend to follow a very similar plan in order to seduce others to their cause—which often involves forcing someone into taking their enemy’s life. Palpatine continually offered his potential apprentices the same options, first with Dooku, then with Vader, and finally with Luke. But while Dooku killed Yaddle, and Vader killed Dooku, Luke was the first to refuse. Despite Palpatine’s plan working perfectly for Count Dooku in Tales of the Jedi and Darth Vader in Revenge of the Sith, Luke alone saw through Palpatine and his grand scheme and realized that if he killed his father, he would simply have been replaced down the line as the others had.