The difficulty curve... what in the world is it?

So, I thought I’d figured this out, and it turns out I haven’t. I’d like to get a real sense of what the difficulty “should be,” what it’s meant to be, and I seem to be finding a large number of answers.

Here’s the various descriptions of difficulty that I’ve found so far:

From Burning Wheel Gold, page 15:
OB 1 “A simple act done with little thought.”
OB 2 “An act performed routinely at your job.”
OB 3 “An act you can accomplish if you concentrate.”
OB 4 “A risky act.”
OB 5 “An act that requires expertise.”
OB 6 “An act that requires a heroic effort.”
OB 7 “An improbable feat.”
OB 8 “An act requiring preternatural ability or a lot of help.”
OB 9 “An act deemed nearly impossible.”
OB 10 “A miracle.”

However, according to the Burning Wheel GM screen and the wiki introduction to the rules:

Ob 1 Easy
Ob 2 Routine
Ob 3 Difficult
Ob 4 Extremely Difficult
Ob 5 Master-level
Ob 6 Heroic Effort
Ob 7 Ludicrously Difficult
Ob 8 Nearly Impossible
Ob 9 Phenomenally Difficult
Ob 10 Miraculous

Almost identical to the GM screen and wiki introduction is the Monster Burner, also page 15:

Ob 1 “Easy or simple tasks.”
Ob 2 “Routine everyday stuff.”
Ob 3 “Difficult.”
Ob 4 “Extremely difficult.”
Ob 5 “Master-level (ye olde beheading with one cut)”
Ob 6 “Requires a heroic effort.”
Ob 7 “Ludicrously difficult.”
Ob 8 “Nearly impossible.”
Ob 9 “Phenomenally difficult.”
Ob 10 “Miraculous.”

I’ve done a probability sheet here.

I’ve also gotten some feedback on this thread, from user Wayfarer:

(emphasis in original, changed italics to bold for visibility)

The difference between Burning Wheel Gold and… well, everywhere else is staggering. I’m hoping to get a sense from other players as to what you guys find the actual best sense of difficulty for the OBs, based on experience.

What is staggering about the difference? The descriptions you listed read nearly the same to me, although the BWG version is simpler for me to imagine, but that’s probably a personal preference thing.

Go with Gold. Always go with Gold.

Khana, you seem to be getting hung up on math in a way I don’t really grok. Underneath all the objective math is a sea of subjective abstractions. Let’s say I’m playing and I try to climb a cliff. That climb is an unknown difficulty. You get to tell me how difficult it is. You could say this is a pretty difficult cliff, Ob4. That may be horrendously challenging for me and my Climb B2. Or Let’s say you look at my Climb 2 and say "You find a place that looks climable, but it’s still going to be hard for you, Ob2. That’s still a climb I’m probably going to fail, right. But, Thats now my problem. I get to FoRK in other skills, and maybe I’m Mountain-wise. And I could have die trait or a call-on. Plus I’m carrying some Artha. And, you get to set the terms of failure. Falling to my death is a different level of fail from being spotted on the way up. But, ultimately there’s no objective cliff climbing difficulty so your initial choice depends on what role you want this climb to play in the overall game session. There’s no wrong choice there.

If I may quote myself…

So keep in mind that difficulty is relative to what you want to make difficult in this particular game, and that tuning those Ob knobs is a big part of setting up the game expectations.

And I stand by what I said. Ob 1-3, maybe 1-4, should be most tests for most games, at least until everyone’s always doing crazy stuff after a year or more of consistent play and increasing stats. There will be harder tests, of course, but they should stand out as the exception, not the rule. Because those harder tests are hard and should hurt.

I’m also not seeing a staggering difference between the first table and the other two. They appear nearly identical to me.

Edit: Maybe this will help?

I really appreciate the insight into the difficulty curve.

Noclue, a major reason I’m hung up on the math is that we’ve got this other game: it’s presently in an abomination, chimera ruleset, primarily based on Pathfinder rules that’s been running for about 6 years now. As we’re increasing in level (we’re presently level 9, it’s been kept a low level game for a loooong time), we’re increasingly running into major, major problems with the pathfinder rules, for the vision we have of the world.

Burning Wheel seems like a fantastic replacement. We’ll still need to alter things, however. On that list, is we’re using the Magic Burner to create our own magic system. This is proving extremely difficult, and the biggest challenge we’re facing right now is getting the right sort of difficulty established.

We’re taking about 3 months off of our regular game, since it’s at an excellent point for this transition. For the next three months, we’re going to go nuts on Burning Wheel rules - we’ve already been playing a Burning Wheel game for about 6 months now, and are comfortable enough with it that we feel confident this is the right choice, and confident enough in the rules (and what rules variations we’ve implemented) that we think now’s the best time.

The regular game is very much high-magic, and it feels like an absolutely insane balancing act. Part of the challenge is the fact that, in BW rules, skill and power are synonymous. In our game, it’s decidedly not. Finding a way to balance the relative difficulties is driving us mad, and we keep looking at the BW difficulty, compared to the odds, compared to how BW handles failure, and have had incredibly long - though fascinating! - discussions.

The last two responses, by Wayfarer and noclue, have been especially helpful. I really appreciate it.

Thanks for the link!

It’s really just the difference in difficulty for OBs 3, 4, and 5, now that I look at it. Just those seem to be particularly important, since they’re going to be somewhat commonly rolled.

For OB 3, you have “Difficult” and “An act you can accomplish if you concentrate.”

From BWG:

Exp 3 = “Nominally trained and practiced.”
Exp 4 = “Competent; everyday stuff doesn’t pose a challenge.”
Exp 5 = “Expert.”

With Exp 3, you are trained and practiced, you’re in the regular sort of threshold of skill (3s and 4s are normal, as I understand). Yet, you have a paltry 12.5% chance of success.

With Exp 4, you’re supposed to be competent. But if something requires concentration, you can only manage it 31.25% of the time?

Exp 5 is outright an expert in the field. Someone who is beyond trained, beyond competent, can only manage really concentrating on a task 50% of the time?

Wayfarer’s point about tailoring the OBs to the intended difficulty threshold of the game (gritty vs crazy heroics) is very helpful. It makes me feel liberated in tailoring the OBs to the difficulty thresholds we want. I just find the clash between the numbers and descriptions a bit… difficult to handle.

Ah, but those numbers are just the skill alone! If something requires you to really concentrate, that suggests to me that you can’t just rush it- you could working carefully, getting help, using exceptional tools, or setting up conditions for success by making a linked test. Furthermore, a real expert would probably have some related skills, and be able to pick up some FoRK dice. I’d an expect an expert (Exp 5) working on a difficult task to pick up another three dice or so from various sources, so you’d be rolling 8 dice, ~86% chance of success. 5 dice is what an expert would be rolling with no prep, no help, ordinary tools, and no expertise in any other related subjects, which hopefully is pretty uncommon!

… you have an excellent point.

And now I feel silly. In the BW games I run, there’s practically never a test that the PCs really want to pass that doesn’t involve at least one extra dice. Well. Um. Haha.

I’m new to BW as well, so this may be way off, but you’re not taking into account all the FoRKs that are likely to be at play here. My carpentry skill may be “Expert - B5” and I’m working on a creating a beautiful chair that requires “Concentration - B3”, but you can be sure that I’m not only rolling 5 dice. For this chair I’m certain to use some combination of “Chair-wise”, “Wood-wise”, “Jig-wise”, “Carving”, another skill or two, maybe a die trait, and we haven’t even brought in any Artha.

This feels about right to me. Experts in their craft rely on a host of skills when putting together something difficult and still make mistakes that they have to recover from or “just get lucky” (almost making a mistake, but catching yourself at the right time…Artha).

Nominally. Which means, roughly, “in name but not so much in actuality”. It is a very important qualifier to understand the scale, in my opinion.

Where those obstacles really hit you hardest are in spell casting.*(no FoRKs) U nless you have some enchanted item to help you along with a die or two you pretty much have use Carefully/Patiently to make the higher obstacles (even with open ended dice).

So, here’s my take on the BWG difficulty curve:

First off, the Monster Burner lists exponent 4 as “the realm of proficiency […] skills you use every day, but are never really challenged.” I will therefore take this as the baseline exponent for something that a character is reasonably good at, but not great or an expert at. So…

Ob 1. “A simple act done with little thought.” A person with a B4 exponent has a 94%* chance of passing an Ob 1 test. Seems about right to me.

Ob 2. “An act performed routinely at your job.” With exponent B4, you have 69% chance of passing an Ob 2 test**. Add in an extra die or two from Artha/FoRKs/help/advantages, and you end up in the 80-90% range. On the other hand, B3 (“basic competency”), yields only a 50% percent chance of passing, and at B2 the probability of success falls to 25% (“just enough to get you into trouble”, indeed). B1 cannot even hope to succeed without help, artha, or some other advantage. Note that Ob 2 will always be Routine for a character with B4, so if you ever want to advance, your going to have to start going outside your comfort zone by taking on higher Ob tests.

Ob 3. “An act you can accomplish if you concentrate.” Here is where things get interesting. B4 alone only gives you a 31% chance of success – not good, but sometimes you don’t really have a choice. Add in an additional die from Artha/FoRKs/help/advantages, however, and your chances rise to 50% (even odds), and two extra dice will bring you up to a much more manageable 66%. The bottom line is, in order to stand a better than even chance of passing an Ob 3 test, a reasonably proficient character is going to need to get help, use FoRKs, take advantage of situational advantage dice, or spend artha. That is to say, they’ll have to concentrate. For this reason, I am personally of the opinion (shared by a number of people on these fora) that Ob 3 should be the default level of obstacle that the GM should throw at the players. Because it’s just challenging enough to force the players to engage with the system and fight for every advantage they can get, without being insurmountable. This preference for Ob 3 tests, of course, is informed by my preference for grittiness in my Burning games. If you want something less gritty, then you should probably default to something around Ob 2.

Ob 4. “A risky act.” A character with a B4 exponent, without artha/help/etc., has only a 6 percent of passing this test. To stand even a 50% chance of passing such a test, you’re going to need to marshal 3 extra dice (for a total of 7); one or two won’t cut it, yielding 19% and 34%, respectively. Risky, indeed.

Ob 5. “An act that requires expertise.” A character with a B4 exponent simply can’t make this test along. He’s going to need help, advantages, FoRKs, or artha, and even then, the odds aren’t very good. 9 dice are required to have even odds of passing, requiring a character with B4 marshal 5 additional dice. Even nominal experts (B5) only have a 3% chance of passing unassisted, though once the players start getting skills in the B5 range, they’ll going to have an easier time marshaling additional dice, as B5 help yields two help dice, rather than only one.


*All probabilities generated using the binomial calculator at

**Remember, dice pools are binomial not normal, so the mean and the median are not the same. Thus, rolling 4 dice will, on average, yield 2 successes, but the actual probability of rolling 2 or more successes on any single roll is greater than 50%. This is because binomial distributions are discrete, so we can’t just cut the probability mass function down the middle like we could with a continuous distribution. Statistics is weird.

Another important thing to keep in mind is that one rolls the dice only when the outcome is consequential. While one might criticize the odds of making a specific obstacle as having too great a chance of failure, but those odds only apply when the task matters. Performing a Routine task is usually, well, routine, that is, inconsequential, so we don’t roll.

When there is something at stake, there is generally more chance of failure. Or perhaps more precisely, we are more interested in failure.

Smeelbo Baggends
Abuser of BBcode

Careful, though. Routine things can matter too, and you can find yourself cheating players of low Ob tests for opening new skills and advancing low ones.

I don’t know.

GM: “this is an easy fire to set, Ob1. Failure here means you get it started but Lord Vance makes note of your lack of aplomb.”

It’s hard to quantify a simple difficulty curve because failure is never just a flat failure. Keep in mind, on a failure, your basic task might succeed, it’s the stated intent that fails. And this is best expressed as a complication rather than an outright failure. Noclue’s example above is but one such. In a strictly binary resolution system many BW failures would count as successes, so the issue is muddied a bit. This is the beauty of many “modern” systems like BW and DW. They aren’t strictly binary. I believe this is the crux of failing forward, and all that.

Whether you have to roll or not is not decided by the difficulty of something. Starting a fire might be easy, but the consequences of doing it wrong serious. You roll. Or it might be very difficult, like lighting a campfire in a drenching downpour without flint or steel… but who cares? If you’re cold as well as wet, you spend the night cold and wet and move on. Don’t roll.

Sometimes it’s also worth some “soft” calls for rolls even when there aren’t BITs on the line when a skill just hasn’t been tested and probably should be at some point. If you’re traveling all the time, you can ask for an Ob 1 roll, or even just count all that travel as practice.

Yeah, the moment you think it’ll be a good idea to “make a campfire so that we have a safe night’s camp” (badly formed task and intent, but gist is there) comes only slightly before you realise rolling so many 1s on a test with failure condition “set the heath aflame” might change some of the game’s current stakes.