In Thor, there is a scene where you can see what looks like the Infinity Gauntlet in Odin's vault. Later (in Avengers: Age of Ultron, IIRC) you learn that Thanos actually has the Infinity Gauntlet, raising some questions about the one in Odin's vault, which are answered in Thor: Ragnarok when Hela sees it in the vault, knocks it over, and proclaims it to be a fake.
After all this, Kevin Feige talked about how the Gauntlet in Odin's vault was originally mostly just an easter egg, but also gave an in-universe explanation for Odin having a fake Infinity Gauntlet; essentially that Odin was pretending to have it so people on Asgard wouldn't worry about it being used against them.
However, in Infinity War, Eitri tells Thor how Thanos came to Nidavellir and forced him to make the Infinity Gauntlet, then killed everyone and chopped off Eitri's hands, putting an end to everything there. It seems that no one was aware that Nidavellir was shut down or that any of this had happened, and seeing as how the Gauntlet was made for -- and went directly to -- Thanos, how did Odin come to know that it even existed and get details of what it looked like in order to create a fake for his vault?