On the other hand, there are plenty of games that give you a set of numbers up front as a basis to let you (the GM or the players) eye-ball the numbers and set your own DCs accordingly - R. Talsorian's Cyberpunk 2020, for one (I think it was the first game I played that used the idea).
How do we set these difficulty-based target numbers?
Decide what difficulty types you want - they should be clear and memorable, and not too many. There should be no doubt which is harder and which is easier.
I'm going with:
- Easy (little chance of failure),
- Average (trained people usually succeed, but may fail),
- Hard (trained people need a few attempts to succeed),
- Heroic (little chance of success), and ...
- Epic (even elite trained people usually fail).
Now we need to look at the numbers we should assign to these.
"Easy" should be at least a 50% chance of success even to untrained and untalented characters - so in the d20 system, that's a 10 (you can beat a 10 on an unmodified 1d20 roll 50% of the time).
"Average" should be about a 50% chance for someone with innate talent, or training. In d20 games, a starting character can have a maximum skill bonus of +4, plus their ability score bonus (again, a maximum of +4, but those sort of scores are relatively rare). So we can set the Average task number at 15, because you need to roll an 11 if you have a bonus of +4, which is what we expect an unexceptional starting character to have.
"Hard" should require talent and skill, and maybe a little more experience. The starting character's maximum ability + skill bonus of +8 can be boosted by Feats like Skill Focus, or by proper tools - so we can set this target number as 20.
However, so far, each of these difficulties can all be beaten by someone with no training, if they're lucky - i.e., they get a high roll. Even an average unskilled person can achieve a hard task sometimes - it'll just take more tries.
"Heroic" and "Epic" tasks are out of the reach of the untalented and untrained.
Let's set "Heroic" at 25 - to beat this, you'll need to roll high, and have a big bonus. That maximum starting character bonus of +8 we looked at a moment ago will need to be boosted with experience or other bonuses to get to the point where Heroic tasks are routine. To have a 50% chance of beating a 25, you'll need a +15 bonus - requiring Feats, experience levels or special tools to reach.
"Epic" needs to be harder, but not out of reach of higher level characters. Let's set it at 30 - that way, Epic tasks won't become routine until you've acquired a +20 bonus.
I've picked increments of 5 for each of the difficulties. Nice and easy to remember, and supported by the game's mechanics: a +5 bonus is normal for a starting character's speciality, and it can be expected to increase by an average of 2 points per level.
- Easy 10
- Average 15
- Hard 20
- Heroic 25
- Epic 30
With these numbers set, instead of having to look up the skill, you just have to agree the class of difficulty.
ProblemsOf course, it isn't perfect - it needs some tweaks to make it work universally. I'll look at solutions to these in future posts, but first, I'll state what the problems are.
Fixed difficulties can make it hard to model tasks that require advanced training.
For example, if someone wants to open a lock, the GM might think "This is just an ordinary door in a house - the lock is nothing special. I'll make it an average task, 'cause the lock is just an average object." However, this would mean that an untrained person with a decent Dexterity could open the lock with a few tries - not very realistic.
D&D and many other d20 games deal with this by saying that some skills cannot be used untrained - if you've not invested your skill points in the skill, you just can't do it. Me, I don't like that so much, as it adds another level of look-up: which skills are prohibited to untrained characters.
Fixed difficulties don't account for circumstances.
If you're trying to break that lock by torchlight, with a kitchen knife and a bent nail, while the rest of your team are fighting a rear-guard action at your back, it's harder than if your were doing it on your table at home under a bright lamp.
This is simple enough to fix - we can make a system of bonuses and penalties to apply. But again, we need to keep it simple!