During Star Wars' Prequels, it took Palpatine years of planning to turn Anakin to the dark side. So, why did he believe Luke could turn so quickly?

From Palpatine and Anakin's first meeting in Star Wars, the Sith Lord saw great potential in the young boy.

And after nearly 20 years of befriending young Anakin and watching over him as a father figure, Palpatine finally felt confident enough to spring his plan into action. 

With years of careful manipulation, he wiped out the Jedi Order and turned Anakin into his apprentice.

 While Vader had become his loyal guard dog, Palpatine grew to despise his pupil for never living up to the "Chosen One" potential.

And by the time of Star Wars: Return of the Jedi, the idea of a much younger apprentice who was also part of the powerful Skywalker bloodline was incredibly appealing to the Sith Lord.

Yet, rather than spending years tricking Luke and spreading doubt, he just brought him to his throne room for a meeting and bluntly told him to turn to the dark side. 

Usually, whenever someone met Palpatine for the first time, he would act weak in an attempt to be underestimated.