After deciding that 3d6 is a dice mechanic that gives good, generally predictable results and a good granularity, let’s work on task resolution. “Task resolution” is any situation where a character is attempting to achieve something, but the mechanics will be used for other decisions as well. One example might be random encounters, where the probability is dependent on, say, weather or the time of the day.
I’ll start with skill checks because this is a large, fundamental part of the game, and what we decide here directly translates into character generation – the first “module” of a hypothetical RPG system that would be worked out in full detail.

First, let’s recall the table of probabilities for possible dice results for a system where your goal is to achieve a certain number or a higher result.

 Roll X or higher Probability 3 100,00% 4 99,54% 5 98,15% 6 95,37% 7 90,74% 8 83,80% 9 74,07% 10 62,50% 11 50,00% 12 37,50% 13 25,93% 14 16,20% 15 9,26% 16 4,63% 17 1,85% 18 0,46%

So a target number of 3 is obviously an automatic success, a target number of 19 or higher is impossible. Of course some factors could help or hinder a character and the dice roll might get modified to make a 3 hard to achieve, or a 19 or higher possible.

Situations should be categorizes into general levels of challenge, or “difficulty”, since the connection between percentages and 3d6 dice roll results may not be readily evident. “Sure, that’s hard thing to do” is much more intuitive than “Roll 5 or higher”. It allows a game master to make a snap decision – “Picking that lock is Easy” – and then throw in modifiers – “but you get minus two because you lack decent tools” – to match the specific situation.

Some difficulty levels are:

• Trivial: Tasks in this category are trivial for everybody, and you wouldn’t roll for them, ever, unless there are several adverse factors involved. For example, walking on the deck of a sailing ship without falling overboard is trivial – unless the ship is being tossed about by twenty meter high waves.
• Easy: This category covers actions that are trivial for a trained professional and easy for everybody.
• Routine: Tasks that that are easy for trained professionals, but challenging for someone without training.
• Challenging: Skilled professionals usually succeed, and when they fail they do so without spectacular problems. difficult for an amateur, and very hard for an unskilled person.
• Difficult: Difficult for a professional, almost impossible for an amateur, and impossible without training.
• Very difficult: Considerable challenge for trained professionals, practically impossible for everybody else.
• Impossible: Exceedingly hard even for a well-trained professional.

As an aside: Are my semantics correct – is difficult/very difficult tougher than challenging?

Either way, let’s assign some numbers to these difficulties:

 Difficulty Probability Roll 3d6 Trivial 100% 3+ Easy 95% 6+ Routine 80% 8+ Challenging 60% 10+ Difficult 40% 12+ Very Difficult 20% 14+ Impossible 0% 19+

The easiest way to work this is probably to modify the dice roll with the character’s skill level as well as any other factors that might apply. For example, reading an ancient inscription may be Routine, unless it’s also dark. Our heroes have only inadequate light sources with them, so the game master decides to slap on a -3 Dice Modifier. In effect, this means the player would have to roll 11 or more, for a 50% chance of success.

Let’s see how this looks if we streamline it a bit – make the difficulties 3 points apart on 3d6.

 Difficulty Probability Roll 3d6 Trivial 100% 3+ Easy 95% 6+ Routine 74.07% 9+ Difficult 37.5% 12+ Very Difficult 9.26% 15+ Impossible 0.46% 18+

Assuming that a “trained professional” has a few skill levels (however we define skills eventually), this matches my initial definitions fairly well. “Trivial” is automatic for everybody. “Easy” is going to be absolutely automatic for anybody with any skill whatsoever, and even untrained individuals won’t fail often – 5% of the time, unless circumstances make the task harder.

For Routine tasks, however, untrained will fail almost 26% of the skill checks. I’d say that’s okay. Imagine if I had to drive a car; I have absolutely no training but of course I picked up a few general principles from observation alone. I could probably figure out how to get the car to move forward, if I am not rushed. But get me into traffic and I am almost guaranteed to cause an accident And forget about a busy highway. Someone who has driven cars for a few years though doesn’t even waste time thinking about driving the car, it becomes second nature to him.

Difficult tasks are… not quite difficult. With a 37.5% success rate, someone without any training will still succeed at one out of three attempts. I wonder if that isn’t too high a percentage. Still, someone with a few skill levels could easily push success chances around. Add a +3 modifier, and success is now 74.07% – what we defined as “Routine”. That fits quite nicely if +3 is a skill level that takes 2-3 years to pick up.

Very Difficult has only a 9.26% chance of success. The area where the odds are so firmly against you, that it’s too much of a gamble if anything important depends on it. Since the initial definition called for “considerable challenge for trained professionals and practically impossible for everybody else”, I’d say this fits reasonably well.

Finally, Impossible, is up 0.46% from 0% success rate. This is really “exceedingly hard” for even someone with some skill levels. Take the +3 from above, which may represent several years of training. They’d move the task to a “Very Difficult” level with less than ten percent success rate. Even another +3 would only push your chances to 37.5% – that may represent 4-6 years of training and the odds are still against you.

So, yes, I think this will do nicely. We eliminated one level of difficulty, but we gained a nice progression of 3/6/9/12/15/18 – easy to remember and work with. The only percentage that I am not quite convinced by is the “Difficult” category; it seems that an amateur has too high a success chance. Still, this is a minor issue best left for playtesting. I think we’re on to a decent basic system.

The next step now seems to be definitions of skill levels. We’ve already made some assumptions, above – a +3 modifier to your dice roll could represent 2-3 years of professional experience. It probably needs to be just a tad higher, but I’ll look into that in more detail next time.

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