I read an interesting article, and the following is a statement by Leslye Headland, the showrunner of "Acolyte".
"When Qui-Gon fought Darth Maul on Tatooine, he immediately realized that he was a Sith and reported it to the Jedi Council. Yoda also knew the code of two, that is, that (the Sith) are always two people, a master and an apprentice. The Jedi thought that the Sith were extinct, but they had some knowledge of the Sith. I don't think it was from ancient history. The fact that he found out that information so quickly made me think that it must have been about 100 years in the past."
The Sith are Force users who broke away from the Jedi Order in the first place.
So, like the Jedi, there is "one apprentice at a time".
The Jedi and the Sith have many similarities.
Yoda is well aware of the past when the Sith broke away from the Jedi Order, so he suspects that the Sith are also connected to the Jedi Code.
Yoda said that the rule of two people established by the Jedi kept the Sith Order alive.
The Sith abused the Jedi doctrine and rules.
Regarding the "rule of two," the Jedi organized many pairs of people, but the Sith only had one pair.
By limiting it to one pair, the Sith were able to ensure the succession of power and avoid cannibalism caused by power struggles.
Yoda: "Only the Dark Lord of the Sith knows our weaknesses."
The fact that the Sith defected from the Jedi Order means that the Sith know the Jedi well. In other words, they know their weaknesses. That will also be passed on.
Qui-Gon: "I have encountered a highly skilled Force user," "He is well versed in Jedi martial arts."
Darth Bane: "Two is good. Nothing more, nothing less. One who has the power. The other who craves it."