system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] How did Yoda, in either Legends or Canon, know of Darth Bane’s Rule of Two during the events of The Phantom Menace?

It is the belief of the Jedi that the Sith have been extinct for 1000 years. 

Darth Bane lived 1000 years ago, and remade the Sith under his Rule of Two. 

How did Yoda know of the Rule of Two to reason there would be no more or less than two total Sith.
gpt
The Jedi have been vigilant for any presence of the Sith Order. When they do find one and raid its lair, they gather lore and artefacts. Throughout all the post-Ruusan literature they've acquired, the concept of "the Rule of Two" consistently appears as it pertains to masters and apprentices.

The Order can't verify that the Sith are truly extinct, so they must remain vigilant, guarding an entire galaxy from the possible influence of just two sapient beings.