In the third session of the DW beta campaign I'm running (available on my podcast, if anyone wants to listen) the thief in the party said he was examining something for traps. It sounded to me like he was obviously intending to use his Trap Expert move ("When [you] spend a moment to survey a dangerous area, roll+DEX..."), but as the GM I was following my prep and knew that there weren't any traps on the thing he was examining. I felt a little weird, because I didn't think it felt fair to expose him to the danger of failing when there was no point to succeeding, so I wanted to say "you don't need to roll for that, there aren't any traps here", but that also felt wrong to me since I thought he was obviously trying to use his move, which calls for a roll of the dice. I "resolved" the situation at the time by interpreting the fiction as if a Discern Realities was warranted, but it felt like I was fudging something when I did that, and it did force him to roll his worst stat instead of his best. (Now that I read the move's trigger explicitly, I think I may have accidentally done it right, since the "dangerous area" part of the fictional trigger didn't apply).

In the fictional positioning thread, Zac offered this opinion about how certain things should be adjudicated in the game:

the game works better if you use only use Moves when a risk of failure would be interesting. Yep, that's the GM's call, big time, but I find myself frequently letting people do harm as indicated (or whatever) because there's no "seed of uncertainty" that could make things go awry.

To me, that sounds like "say yes or roll the dice", a principle which games like Burning Wheel embrace. My reading of Dungeon World is that the GM isn't the arbiter of whether a roll is warranted, but is an interpreter of the fiction like everyone else:

The basic rule of moves is: take the action to gain the effect. To make the mechanical aspect of a move happen the character has to do something that triggers that move. Likewise, if the character does something that triggers a move the mechanical portion happens.

One of the consequences of that (at least the way I interpret it) is that it isn't the GM's job in DW to decide if certain actions are "important enough" to warrant dice rolls, but that the dice rolls always happen in the fictional situation and therefore might become important even if we don't think they're that big a deal before we roll. Is that the way other people interpret it? How would other people have handled this situation? Would that change if the move were something like "when you spend a moment to survey an area for potential dangers" instead of the "dangerous area" thing is says now?