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Appendix B

Working Figures

Nine results from Appendix B, each built as a small machine whose motion is the result. Every figure runs on its own; move the pointer over it, or focus it and use the arrow and number keys, to take over. The numbers on the figures come from the same models; those the book prints are checked against it, and values it does not give are marked illustrative in each caption.

Each figure opens with a few everyday questions; after it come plain words, the reasoning and some thoughts on living, with the mathematics folded away at the end for when you want it. The models are simplified on purpose, and the thoughts on living are directions drawn from them, offered for you to try on. They are not medical, psychological, legal or financial advice. Your life is richer than any model, and the final judgment is yours.

Fig 1 · Appendix B.5

Feedback loop

Start here

  • Have you ever held a view so long that everything you saw afterward seemed to confirm it?
  • When someone points out a mistake of yours, do you usually wave it off, take it in, or swing straight to the opposite view?
  • Can correcting yourself too hard ever make things worse?

Bias as a loop on a chart recorder: the correction lever γ keeps κ = α + β − γ between −1 and 1; too little and the bias runs to the stop, too much and it swings apart.

In plain words

Today's bias carries into tomorrow, what you already believe adds to it, and correction pulls it back. Add the three together and you get one number, κ. Above 1, the bias grows every day; between −1 and 1, it fades back to zero; below −1, you overcorrect and it swings back and forth wider each time. Lucidity here is the correction, and it helps only in the right amount. The numbers are illustrative: the book gives none.

Why it holds

Each round multiplies the last round's bias by the same κ. Multiplying again and again shrinks a number only when its size is below 1, so |κ| < 1 is the whole condition for the bias to die out, and the sign of κ decides whether it fades straight back or swings. Correction γ enters κ with a minus sign, which is why lucidity can pull κ into that band and can also push it through the far side. The machine is a chart recorder because the result is about a path in time: the paper shows every round at once.

For thinking and living

Bias needs no villain. When yesterday's view and today's beliefs feed it more than you correct it, it grows on its own. The figure suggests two habits. Correct a little every day, the way a driver keeps adjusting the wheel, instead of waiting for a crisis. And watch for overcorrection: if each fix lands you further out on the other side, a drift has become a swing. In a quarrel, an investment or a diet, the useful question is the same: am I damping this, or feeding it?

A gentle note

A real mind is more than one number, and κ here is illustrative. Use the picture as a mirror for noticing patterns, and be gentle with yourself: everyone carries some drift, and noticing it is where correction starts.

For advanced readers: the mathematics
  1. Why is |κ| < 1 both necessary and sufficient for the bias to die out? What changes if κ varies from round to round?
  2. Correction enters κ with a minus sign. For given persistence and reinforcement, which range of correction keeps the bias stable, and what happens at exactly κ = −1?
  3. Add a random shock each round. How does the long-run spread of the bias behave as |κ| approaches 1?
Read the section · Appendix B.5