In addition to what the others have said, I think degrees of failure are often a fun thing to introduce whether they are in the rules or not (I’ll assume D&D 5E). It might be that a 20 with your +3 athletics isn’t enough to completely leap over that huge gap, but you manage to grab a handhold a few metres below the edge. You’ll have to take a turn or two to climb up, but you’re okay. The cleric’s roll of 3 with a -1 athletics, on the other hand, sees him plummeting to the bottom and taking a heap of fall damage
In addition to what the others have said, I think degrees of failure are often a fun thing to introduce whether they are in the rules or not (I’ll assume D&D 5E). It might be that a 20 with your +3 athletics isn’t enough to completely leap over that huge gap, but you manage to grab a handhold a few metres below the edge. You’ll have to take a turn or two to climb up, but you’re okay. The cleric’s roll of 3 with a -1 athletics, on the other hand, sees him plummeting to the bottom and taking a heap of fall damage
Yep, those are all great responses. I learned a lot.
Funwise, it seems like a good solution would be “failure… but!” approach.
So the player have at least some reward for doing the best they can even if it’s not enought to clear the chalange completely.