When we all first met Yoda in The Empire Strikes Back, we discovered he was a powerful Jedi but never really got an explanation for why he was living on Dagobah. On the surface, it seemed he was just a hermit who had grown old on a desolate planet and, for the most part, that was explanation enough for fans.
The Star Wars prequels later confirmed Yoda was a key part of the Clone Wars and we even witnessed his battle with Emperor Palpatine at the height of both their powers.
After failing to defeat the Sith Lord, the Jedi Master decided to exile himself to the swamp planet and, unlike Obi-Wan Kenobi, it doesn't appear he ever left or embarked on any adventures (beyond communicating with Qui-Gon Jinn).
Still, we've long been curious about how Yoda hid himself from Darth Vader and the Emperor, particularly as it doesn't appear he ever cut himself off from the Force.
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The newly released book, From a Certain Point of View (which is a collection of short stories set during Return of the Jedi) confirms it's all because of the Dark Side cave that Luke battled "Darth Vader" in on Dagobah.
As we first explained on SFFGazette.com, a story titled "The Light That Falls" reveals Yoda had to use his power to subdue the darkness in the cave, creating a balance in the Force to ensure he remained hidden. Mustafar isn't too far from Dagobah, so this also explains why Vader never sensed his old friend.
We're guessing this is also why Yoda became so unwell as countering somewhere so strong in the Dark Side can't have been easy, even for him.
Of course, this idea is one that will be familiar to fans of the Expanded Universe as Luke learned something similar when he returned to the cave in Timothy Zahn's Thrawn trilogy. Those stories are no longer considered canon.
Yoda was most recently seen in The Last Jedi and it's unclear whether there are any future live-action plans for him. There had been talk of a spin-off movie several years ago, though we believe it was scrapped when Solo: A Star Wars Story failed to live up to expectations.