My understanding -- as someone who's just watching closely from the sidelines -- is that Dolmenwood expects one to use a method I first saw explained in Knock magazine:
- If you have the tools for the job, the skills needed and no time pressure, there's no roll, because you automatically succeed
- If any two of those are not true, there's no roll, because you automatically fail
- But if only one of those criteria is not met, you roll and see what happens
So the thief with tools and all the time in the world can open any lock, unless this is a super-special lock. But if he's doing it while the king's archers are firing on the group while they try to get away, he needs to roll to see if he can do it under that kind of pressure.
Or, if the thief is dead, but the party has taken his gear (because that's the real old school), the cleric has the tools and the time to open the lock, but not the training, she will need to roll and see if she can muddle through.
If you let characters who ought to succeed automatically do so, old school games (and NSR games like Mothership) become a lot less punishing and dice rolls become more meaningful across the board.