I think auto success or fail should be based more on common sense. Like I'm playing a Rogue/Thief with a background as a criminal. How is it possible for her to fail at a level 5 lock? Sure it is rare, but its still there and feels really dumb. With that said I also really don't like rolling in combat. I know its a D&D thing, but I hate missing an attack when I am standing right next to someone. I'm always like, "How the f**k did you miss that!? Are you blind?"
You are not missing when you are missing. Your blow just doesn't do damage.
And a turn is 6 seconds... All the things you do is in 6 seconds of course you can *miss*... You play shooter games? You also miss sometimes. Just imagine those shooter games be turn based and you have 10 minutes time to plot your 6 second turn...
