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 You would not expect a “twenty-five sigma” day once in several lifetimes of the universe. Goldman’s model was in effect saying, this kind of event ''will not happen''.
-This would be the equivalent of all the molecules in a cup of tea spontaneously jumping to the right at the same moment. The molecules are bouncing around randomly — Brownian motion, right? — and so conceptually they could all jump left at once<ref>it may be that, conceptually, they couldn't — Brownian motion depends on collisions. For all I know, this implies that half the molecules are jumping the other way.</ref>
+This would be the equivalent of all the molecules in a cup of tea spontaneously jumping to the right at the same moment. The molecules are bouncing around randomly — Brownian motion, right? — and so conceptually they could all jump left at once<ref>it may be that, conceptually, they couldn't — Brownian motion depends on collisions. For all I know, this implies that half the molecules are jumping the other way.</ref> but the sheer odds of every single atom doing do at once are so infinitesimally small that it would never happen in several billion lives of the universe. Neither the cup or the tea in it would last that long, of course.
-That there were several such days in a row — in a market history measured in decades, not universe lifetimes — must mean the model was wrong.<ref>It was, for reasons we explore elsewhere.</ref>
+But that is the scale of likelihood of a twenty-five sigma event.
+That Mr Viniar thought there were several such days ''in a row'' — in a market history measured in decades, not universe lifetimes — must mean the model was wrong.<ref>It was, for reasons we explore elsewhere.</ref>
+Now here is the thing. When we calculate probabilities — when we roll dice — we are situations of known risk. That average means something. It is not just that on some some dice the probability is more like ⅐, on others now like ⅕, but on average the dice work out at all about ⅙. It must be true of every individual die..
 Rolling dice to ''determine'' an outcome is is quite
 different. We do not build a statistical model that predicts a ⅙ probability: we build the dice to yield the that outcome. The dice are what [[Nancy Cartwright]] calls a “[[nomological machine]]”: a carefully designed, constrained, hermetically-sealed device, designed to generate a specific theoretical outcome. If over time the dice don’t yield a ⅙ outcome we don't chuck out our statistical model: we chuck out the ''dice''.