In Family Guy's spoof of Star Wars, titled "Something, Something, Something Dark Side," Luke Skywalker's scenes with Grand Master Yoda are reenacted with Chris Griffin as Luke and Chris' gas station manager Carl as Yoda. When Luke/Chris senses his friends are in danger, Yoda/Carl says he shouldn't face Darth Vader because he hasn't finished training, and only an experienced Jedi can fight him. The pupil asks, "Then why don't you go?" The master pauses and then says, "Yeah, you're probably ready to fight Vader."
Love it or hate it, Family Guy had a point about Yoda. Supposedly the galaxy's most powerful Jedi chose to chill all by himself in a swamp while the evil Empire reigned supreme for decades. And as Star Wars canon and lore have expanded with the Prequel Era and the Disney Era, Yoda has become an increasingly questionable character. Thus, while history says Anakin Skywalker was the most dangerous broken Jedi, it could be argued that Master Yoda's actions made him even more broken and more dangerous.
Yoda was introduced in 1980's The Empire Strikes Back as a successor to Obi-Wan Kenobi in the role of Luke's mentor. Audiences expected an even more powerful version of Obi-Wan, but when Luke finally landed on Dagobah, he instead found a goofy green puppet to annoy him. Little did he and audience know the little green guy was Yoda himself, emphasizing that "size matters not." Luke and Yoda's scenes are some of the best moments in the franchise, and the little green puppet became arguably its most beloved character. His quotes and backward style of talking continues to be mimicked to this day.
The oldest, wisest and most powerful Jedi in the galaxy witnessed the Jedi's downfall with Order 66 and the subsequent rise of the Empire. While Obi-Wan Kenobi defeated and severely disabled Anakin Skywalker in 2005's Revenge of the Sith, Yoda battled Emperor Palpatine in the Chancellery Secretariat, but fell just short of slaying him. After being rescued by Bail Organa, Yoda went into into exile stating. "Failed, I have." The Jedi master clearly took the defeat and the fall of the Jedi very hard, and that would be the last duel of his life.
Afterward, Yoda and Obi-Wan decided that hiding Anakin Skywalker's newborn twins would be enough to one day restore the Jedi Order. Bail Organa and his wife adopted and raised Leia, while Obi-Wan delivered Luke to his Uncle Owen and Aunt Beru on Tatooine. Although Luke and Leia are the two most important characters of the classic trilogy, and it's fitting that the last of the old Jedi rely on them to save the galaxy, the expanded Star Wars canon shows they could have done more.
Yoda and Kenobi were not the only Jedi who survived Palpatine's purge. Key characters from the Clone Wars and Rebels animated series, like Ahsoka Tano and Kanan Jarrus, survived and continued to represent the Force during the Empire Era. So why didn't Yoda gather the survivors and take them to Dagobah with him? It could've been his opportunity to rebuild the Jedi while waiting for Luke and Leia to grow up.
The closest Yoda came to imposing his wisdom to a non-Skywalker Jedi trainee was when he reached out to Kanan and his pupil Ezra Bridger on Rebels. He did a good job helping Ezra confront his fears and find his purpose as a Jedi, as well as assisting Kanan in becoming a teacher himself. According to canon, however, that was the only known teaching Yoda did before The Empire Strikes Back.
Despite Yoda's failure to train the Jedi as the beacon of the Force's light side for two decades, according to the anthology From a Certain Point of View, he felt some regret about it. During the events of A New Hope, the lonely Jedi Master lamented he didn't take Leia with him as an infant to train. However, at the time, he felt he was too old to do so.
When Obi-Wan Kenobi's spirit appeared to him to request that he train Luke, Yoda refused, believing Leia was more ready than her brother. Yoda was prepared to die, but was ultimately convinced to train the boy before doing so -- and the rest is history. In their brief time together Luke learned a lot from Yoda, who set him on the path to becoming a Jedi master. Yet, this is evidence that if Yoda hadn't retreated in defeat and instead trained more individuals over the years, the Jedi would have been restored more quickly and the Empire would have been defeated sooner.