Why Did Palpatine Fear Qui-Gon Jinn?

Darth Plagueis and Emperor Palpatine were so fearful of Qui-Gon Jinn that Darth Maul was ordered to kill the Jedi master on Naboo in the Phantom Menace. Why did Qui-Gon instill such fear in two of the most powerful Sith warriors in Star Wars History? If Qui-Gon had lived would Anakin have still turned to the Dark Side? We'll find out in this episode of Star Wars Theory.