Interesting idea here from Lindybeige: that die rolls are less about success or failure and maybe more about revealing the world. His main example is climbing a wall. More than marginally success means this is the kind of wall the character knows she can climb. Because the characters don't know about the die roll - that's a player thing. For the character, it is more "I know I can do this", "I know I can't do this", "I think I can do this", and "I have might be able to do this, and I might not."