I've added that to the post now - a sketch of the original, and what went wrong (simple version: I applied financial/arbitrage insights to utility, whithout realising that the mere existence of investors and arbitragers in the world would change the price you put on something).

Think of it as payback for those who tried (unsuccessfully, until Eliezer's attempt) to point out that perhaps you didn't understand expected utility correctly.

Oh, it wasn't Eliezer pointing it out that made me realise it; it was me trying to prove Eliezer wrong that did the trick.