Triggers happen in-fiction. Never assume a player shares your fiction.
Dungeon World introduces the idea of disagreement between GM and player on what's actually going on in the basic moves chapter. Not explicitly called out as such, which I think is a weakness of the book as opposed to Apocalypse World's explicit mistake-and-correction syntax.
You can see an example of disagreement on which move is being triggered in the Defy Danger section, where the GM thinks the player is defying danger but the player thinks they're attacking an enemy in melee.
You can see an example of the player thinking they can make a move but the GM telling them they can't in the Parley example, where the GM tells the player that a friendly word and a smiling face aren't sufficient leverage, in this situation, for Parley.
And it's also possible that the GM thinks a player is making a move but the player thinks they aren't.
There are two ways the player may not be trying to make the move.
They don't believe they're taking the in-story action the move requires.
Let's suppose the GM describes a room with a mural on the far wall and a cracked floor, and Wizzrobe says he wanders in to inspect the mural, and the GM says:
"The floor beneath you crumbles away, Defy Danger +dex to not fall!"
Wizzrobe is just fine to say
"Wait, that didn't sound dangerous, I thought it was just for flavor like the mural thing."
and the GM can take that under advisement. It's fine to walk that back to a different GM move: tell them the requirements or consequences and ask, like:
"Yeah, deep cracks and you can see places the stone has fallen away. But you can't really examine the mural from over here. Want to risk the crossing?"
But keep in mind -- take it under advisement. Dungeon World is a conversation in which everybody is participating and in which everyone should agree on the facts of the matter at hand. As the GM you have the freest possible hand, mechanically, in doing this, but it's always going to come down to the facts of things as agreed on by everyone at the table.
If this is an important mural and you want there to be a pit trap before it, you can walk things back a different way. You can say "yeah, fair, Defy Danger +wis instead to spot the weakness in the floor before you go plummeting" if Wis is one of Wizzrobe's better stats; this preserves your original intention.
Or, alternately, if you've been explicitly mentioning cracked floors all night and they've always turned out to be pit traps, defy danger +dex, you can remind Wizzrobe of this and he'll probably be a little more okay with it. Maybe give somebody a chance to aid Wizzrobe's roll since the whole party's been experiencing these things all night.
They don't want to obtain the result of the move.
Let's suppose the GM describes a room with a mural on the wall and a cracked floor, which he does not intend to be a pit trap, and Wizzrobe says he wanders in to inspect the mural, and the GM says:
"Sure thing. Spout Lore to see if it jogs your memory any?"
Wizzrobe is also just fine to say:
"No, just, like, what's it look like, what's it made of?"
and the GM can take that under advisement. It's fine to just describe the situation around the players and not reveal anything particularly interesting or useful, because Wizzrobe isn't rolling Spout Lore, like
"Oh, okay. The stone's dyed in pieced-together geometric forms, like stained glass but without the frame or the glass. It depicts a black winged figure wielding a large red sword, surrounded by a throng of small grey figures."
Then keep things going, and offer an opportunity.
"But after all these years you can't make out much more than that. If you want to work out why this was drawn or what it means, you'll need to Spout Lore."
And Wizzrobe can follow up on that or not. I mean, it's not like you can force him to consult his accumulated knowledge.
Again -- take it under advisement. It might be that on reflection Wizzrobe really was trying to learn something interesting or useful about the mural and says so given some more time to think. These calls can often be a little trickier to make, looking for alternatives when your first guess was wrong, but you can usually find something appropriate. It can be useful to "work backwards" in that case - start from what the player is intending to do and find a move with those results.
They're trying to keep the goblins pinned in the fort with a well-placed warning shot? Well, if they don't want to hurt them they don't want to deal class damage, so what they're doing can't be a Volley. But if it seems like a sensible way for things to progress, what move could they be making instead? Well, look at Parley; they're trying to manipulate the goblins into doing what they want, and their leverage is: I could put an arrow through any one of you. You can even impose Volley-flavored consequences on a 7-9, like you have to spend a bunch of ammo demonstrating how you can hit any of the exits, or you have to focus your attention on keeping them contained and miss something else.
But when you choose not to choose, you have still made a choice.
If you describe a threat affecting the players, and they agree the threat is there, and you give them an opportunity to make a move, and they don't take it or offer an alternative, well, they saw a threat coming and did nothing. I'd call that a pretty golden opportunity for you to make a hard move involving that threat.
Some moves, like Discern Realities, are more proactive and don't necessarily have downsides to not take them, and that's fine. But many more moves than that presuppose a player is in a dangerous situation and trying to deal with it somehow. You might as well make the move in that case, as a player. At least you'll get XP as consolation if you fail.
And some things are inevitable.
Apocalypse World has something called "the harm move", which you make when you suffer harm, to reflect the unpredictable nature of wounds. You can't even choose not to make it. You have suffered harm and so you roll.
Dungeon World similarly has Last Breath, which is triggered when you reach 0 HP, and might be the caprice of Death rather than anything you're trying to do, so it doesn't even make sense for you to not roll? And you're certainly free to write custom moves that demand it as well. Like, say:
When you are struck by Dark Jazerain's crimson sword, Lifedrinker--
(Wizzrobe: "Is this a grudge monster? Over a mural?")
--before you take damage, you may voluntarily sacrifice any amount of your own HP. Roll +HP sacrificed, or +0 if you did not sacrifice any.
- On a 10+, your life force burns inside Jazerain, aiding you. Take +1 ongoing to act against her.
- On a 7-9, the sword's thirst is temporarily sated; take +1 armor forward.
- On a 6-, Lifedrinker finds you wanting. Jazerain rolls twice and takes the best result for damage.