Ismaul
Thought Criminal #3333
I thought you were going to highlight the other part of the quote: makes progress combined with a setback determined by the GM.But the thing here is that when you try to climb with DC 15 and roll a 14, it doesn't necessarily mean you fall. Let me quote you the rules:
If the total equals or exceeds the DC, the ability check is a success--the creature overcomes the challenge at hand. Otherwise, it's a failure, which means the character or monster makes no progress toward the objective or makes progress combined with a setback determined by the GM.
If the roll fails, either there should be an interesting consequence, or there shouldn't have been a roll. You don't roll if there aren't multiple possible outcomes. A failed roll can be a pure consequence that still moves the story forward (an obstacle or setback that creates new challenges, or a fork in the story because a door has closed but other paths are open, or just a miss/HP taken in combat), or a success / partial success with a consequence/setback if failure doesn't make sense.
Lagi your GM definitely sucks. Especially for determining outcomes beforehand. I'd never come back to his table unless he was willing to learn and change.