Why Blades in the Dark feels less swingy than d20 – and why the bell curve (and variance) aren't the main reason

prabe said:

I would add that the additional weight Blades tends to put on single given rolls can make the game seem more swingy than D&D, especially given the much-reduced options for the GM to moderate results.

I mean, my experience of Blades is persistently stepping on rakes, as we both know.

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Bill Zebub said:

I suddenly feel the urge to play an RPG called "Stepping on Rakes".

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franz101 said:

After recalculating the numbers, I believe the common explanation "d20 is swingy because uniform distribution vs. bell curve in dice pools" misses the real core difference. The bell curve and variance per roll are largely irrelevant here.The key lies in two other mechanisms:

1. Granularity of progression / how difficulty & competence are modeledIn d20 systems like PF2e the probability curve of a single roll stays exactly the same shape (shifted uniform).
   When your character gets better (+1 bonus) or the task gets easier (-1 DC), the entire curve shifts linearly by 5 %. Every improvement is fine-grained and perfectly incremental.In dice-pool systems like Blades in the Dark each fixed number of dice (1d6, 2d6, 3d6, 4d6) produces its own completely distinct, fixed probability distribution ("template").
   This template cannot be shifted.
   To make a roll easier or harder you switch to a different template (more or fewer dice).
   That means improvements happen in large, non-linear jumps (e.g. going from 2d6 to 3d6 halves failure chance from 25 % to 12.5 %, while partial success stays almost the same).Edge probabilities (worst & best outcome) for Blades (highest die decides):
   • 1d6: 50 % Failure / 16.67 % Success / 0 % Critical
   • 2d6: 25 % Failure / 27.78 % Success / 2.78 % Critical
   • 3d6: 12.5 % Failure / 34.72 % Success / 7.41 % Critical
   • 4d6: 6.25 % Failure / 38.58 % Success / 13.19 % Critical
   At 3–4d6 the edges (extreme failure and critical success) are already in the 6–13 % range – very similar to typical PF2e crit fail / crit success chances (~5 % each).
   This suggests d20 is not inherently swingier than dice pools when looking at extreme outcomes. The bell curve / variance explanation therefore doesn't hold up as the primary reason.
2. Rightward shift of outcome labels (Position & Effect)In Blades, Position (Controlled / Risky / Desperate) and Effect level systematically shift the meaning of the dice results to the right:
   • What would normally be a failure becomes a partial success
   • Partial success becomes full success
   • Full success becomes a critical
   As a result, true hard failure (scene-stopping catastrophe with no progress) shrinks to ~5–10 % or less (often even lower in good position).
   The game stops being about "do you succeed or fail?" and becomes almost exclusively "how well do you succeed?"In contrast, in most d20 scenarios a miss/failure stays in the 40–50 % range – there is no comparable systemic mechanism that eliminates hard failures on that scale.

Summary:
The feeling that Blades is "less swingy" or "more reliable" doesn't primarily come from bell curves, lower variance, or better edge probabilities.
It comes from the combination of
(a) chunky, non-linear competence jumps (switching fixed templates)
and
(b) active, mechanical minimization of catastrophic failure through rightward shifting of outcome labels.This seems to be the deeper design difference that actually explains the player experience – not the shape of the probability distribution on a single roll.What do you think? Am I missing something important here?

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prabe said:

Blades in the Dark capably and amply serves my needs in this area.

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franz101 said:

Rightward shift of outcome labels (Position & Effect)In Blades, Position (Controlled / Risky / Desperate) and Effect level systematically shift the meaning of the dice results to the right:

• What would normally be a failure becomes a partial success
• Partial success becomes full success
• Full success becomes a critical

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Old Fezziwig said:

A 1-3 on a roll with Controlled/Limited is still going to be a failure -- my little dude won't get what he wants, and there'll be consequences

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franz101 said:

After recalculating the numbers, I believe the common explanation "d20 is swingy because uniform distribution vs. bell curve in dice pools" misses the real core difference. The bell curve and variance per roll are largely irrelevant here.The key lies in two other mechanisms:

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SableWyvern said:

A d20 is absolutely more swingy than 3d6 (where swingy means the outcome is harder to predict). However, one of my huge pet peeves is the claim that if a game uses dice that produce bell curves, the game is less swingy/more predictable than one that doesn't.

What range or distribution your dice provide, on their own, tells you nothing about how swingy a game is -- because, in any game, you are not just rolling some dice in isolation, you are typically applying modifiers and consulting mechanics to determine what the output means. Swinginess is determined by the combination of all those factors.

A system where you roll an unmodified d20 looking for 11+, one where you roll an unmodified 3d6 looking for 11+ and one where you flip a coin are equally swingy. They all give a 50% chance of success.

A system where you roll an d20 looking for 6+, with modifiers to the roll ranging from -2 to +4 is far less swingy than either of the two examples above, as the default success chance is a much more reliable 75% and, once the modifiers are factored in, varies from 65% to 95%.

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zakael19 said:

There’s something fascinating about rolling 5d6 and getting nothing above a 3. This lovely little graphic table suggests that’s a 3% chance, so boy did my player feel that. Turned out the dice really wanted that complication to happen.

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zakael19 said:

This is why we kill off the terrible decision that was the idea of Controlled in favor of “pay a cost and move on” .

RISK OR NOTHING BABY

(Man I’m jonsing to run some ‘68, I hated the whole “everything is gloomy and dark and there’s no sun” crap of base BITD so much)

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