I’ve written a lot about this move over the years. I’m going to try to start collecting these on the blog so that they’re easier to find and reference.
I posted this essay on G+ back in 2016. At the time, there was a lot of talk and swirl on the Dungeon World Tavern about whether Discern Realities was a good move, and when it triggered, and how to use it. This was my response.