Early in the development of the Seref System we made the decision that we weren’t going to include automatic successes or critical failures as part of the rules. For a time we allowed automatic successes when play testers rolled a one on skill checks, but this became incredibly muddied when two players each rolled a one in opposed checks. Because we use a D10 system, it’s pretty easy to roll a one, or a ten, moreso than with a D20, where it’s still annoyingly common to see fighters accidentally fling their swords across the room. So rather than have a one in ten chance of humiliating failure, or automatic success that couldn’t be stopped nine times out of ten, we chose to write them out of the game altogether.
Critical failures have never made particular sense to me. The idea that you could have maxed out your ranks in any given skill, but have a one in ten, or one in twenty, chance of an utterly humiliating failure just seems odd. While certainly people do fail, and sometimes in an epic fashion, it’s not often that you see the sort of failures that occur from a critical failure in a RPG happening to professionals in the real world.
As it stands now, a one on a skill check is simply an excellent roll, which provides its own benefits (additional damage, better enchantments, etc). A ten on a skill check is always a failure, but not a critical one. Spells miss their target, weapons swing wide, characters fail to persuade others to lower their prices. Rolling a ten does not, directly, bring harm to a character, as critical failures so often do in other systems.