The armorers accomplishing the knights

An important lesson taught by the gaming approach to warfare is that the superforecaster must be always open to 'unknown unknowns', to use the decision-theoretic jargon popularized by US Secretary of Defense Donald Rumsfeld during the Iraq war.

Nose-blood, Thousand-leaf, Yarrow, is so well known that I need not waste time to describe it.

And then you feel all round your pocket and fish out that absurd little thing, all by itself, sticking on the end of your finger like a tiddleywink. The shop-girl sniffs. She spots immediately that it's your last threepence in the world.