Which is to say that if you're climbing over a wall, and roll a 1, "you land on a bear" is technically a valid response from the MC.

To get to what I love about Apocalypse World, we gotta step back a bit from this. Why is this character rolling to get over a wall? Who is this character, what tools does their player have at their disposal? What dangers are present? What are the stakes?

In Apocalypse World, you don't just roll to "Get over a wall" You only roll when a move with a roll in it is triggered. In Apocalypse World, according to the player facing and the MC facing rules, everything that is happening to and around the characters matters. Who the characters are matters. Their relationships matter. What has happened before matters. Apocalypse World isn't a game of skill checks, it's not a game of "did you do the thing?" It's a game of tense situations with stakes the characters and players care about. It's a game of "What do you do?"

The game gives you a lot of rules to follow and tools to utilize to figure out what happens next. The MC looks at the Fronts, they look at the parts of a scene, they look at the stakes that have been established, and they look at their Agenda, Principles, and moves. Then they use their imagination, or talk it over with the players if they're really stuck.