A low die roll (a "miss") does not mean failure.
Like much of Dungeon World, it's such a paradigm shift that it takes a while to really grok.
In most RPGs, a bad roll means failure—the character failed to accomplish the task. Often this clashes with an awesome character concept, and repeated failures turn the game into a Keystone Kops-esque slapstick fumblefest.
In Dungeon World, a bad roll—6 or lower on a roll of 2d6 plus an attribute modifier—means trouble. As per its GM principle "Be a fan of the characters", a Dungeon World game master's job on a "miss" is not to make the player characters look incompetent. It's to make the world dangerous. (Another GM principle: "Think dangerous.")
Even partial successes are improved: Where in many games a tie or partial success means nothing much happens (e.g. combatants harmlessly exchange parries), in Dungeon World it means success with complications. On every roll the story changes and presses onward.
- On a hit (10+): Your character is a straight up badass!
- On a partial success (7-9): The plot thickens!
- On a miss (6-): This foe/dungeon/adventure/world is dangerous! (And thus your character is a straight up badass.)