So in Dungeon World, the basic mechanic seems to be that you roll 2D6 + Modifier. If you get a 10+, its a 'good' result, and if you get a 7-9, it's an 'OK' result, with <=6 being 'bad/useless'. However, I don't see that there are enough consequences for bad/useless!
Let's take as an example
Hack And Slash. The move works thusly:
When you attack an enemy in melee, roll+STR. On a 10+ you deal your damage to the enemy and avoid their attack. At your option, you may choose to do +1d6 damage but expose yourself to the enemy's attack. On a 7–9, you deal your damage to the enemy and the enemy makes an attack against you.
So 10+ deals damage. 7-9 deals damage but suffers an incoming attack. <7? No effect. So oddly, it seems you suffer less damage with a complete miss than you do with a hit of some sort. On top of that, rolling <7 gets you free XP! What is the downside to players deliberately spamming moves that they know will not land in order to 'farm' XP?