system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] Could Qui-Gon Jinn have tried appearing as a Force Ghost to Vader to attempt to guide him back to the Light Side? Would there have been any risk in taking this approach?
gpt
Qui-Gon died before finishing his training/preparation in becoming a Force Ghost. He was unable to appear visually without help from other Force Ghosts. However, as he was the first Jedi to have success in millennia, he was alone until Obi-Wan and Yoda and Anakin joined him. Together he was finally able to appear to Luke with their help after the death of the Emperor.

What he *did* do was appear as a disembodied voice both to Yoda and Qui-Gon, and taught them how to become Force Ghosts. With his guidance they were able to fully complete their training, and become full ghosts.

So by the time Qui-Gon could *appear*, Vader and the Emperor were dead. He *could* have spoken to them, like when he tried to stop Anakin from slaughtering the Sand People, but probably wouldn't have accomplished much. 

Plus, who knows what the Emperor was capable of if he were to discover the existence of the Force Ghosts. This unique Light Side ability is arguably the single most powerful technique there is! To live after death, able to communicate at will with the living across the galaxy, able to train and assist their followers for years. All while being invulnerable and perhaps even immortal (so to speak). With this technique the Jedi could be totally wiped out, and return from the grave over and over. Unless the Emperor had someway of disrupting it, like he clouded the Force during the Clone Wars. The Jedi couldn't risk jeopardising their greatest weapon, and their own afterlife, just to "talk them out of it".