I've been looking at designing an RPG system lately and I'm currently considering where to set the "difficulty" of a roll at to get some satisfying results.
I'm wondering - has anyone researched some "average" RPG probabilities that "feel good"? My guess would be having something like a 50% success chance as a baseline, then turning it up to something like 75%, 87.5%, etc. as proficiency goes up seems to at least sound good on paper, but it would be nice to have a comparison to some games out there.
I'd be interested to know what kind of probabilities have a good "game feel" - how difficult ought it to be to succeed at a roll of some task you're new at, something you're proficient at, and something you're a master of for example.
I know that in systems like D&D your to-hit bonuses and enemy defences both scale, and many games like PbtAs have a somewhat static difficulty. I'm wondering if there are any design docs for roll probabilities, or does anyone have their design experience to share on such numbers?