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