Mr Market quotes, you decide

Look at what changed between day 1 and day 4 in the figure. Halden sold the same tiles from the same three showrooms to the same builders. Its owner earnings were still about 1.00 million a year. The only thing that moved was the partner's offer, from 10.0 million for the whole to 16.6. That move tells you something real, but what it tells you is about him: on day 4 he felt good. It does not tell you that the business became worth 6.6 million more over a long weekend.

This is the reading Buffett gives the allegory in his 1987 letter. The partner's offers swing with his emotional state, not with the business, and the letter's line for how to treat them is the one to keep: "Mr. Market is there to serve you, not to guide you." A quote serves you when it hands you a chance to trade at a price far from your value. It guides you, wrongly, when you let it tell you what the value is.

The most underrated feature of the partner is that he does not mind being ignored. You are never obliged to accept his offer, and declining it costs you nothing that you own. Your slice of Halden still earns its share of the owners' cash whether or not you looked at the quote today. That is the asymmetry that makes the allegory useful: he must quote, you need not answer.

The cost of ignoring him is only an opportunity cost on the rare days his offer is far from your value, and those are the days your written zones flag (Part 2). On every other day, not answering is the correct and complete response. People who feel they must act on every quote are paying, in attention and in mistakes, for a service that was offered for free.

In a listed company the partner is the market itself: a stranger's bid appears every few seconds whether you want one or not. Halden is private, so the page makes the cousin play him, constructed, for two weeks. The behaviour that matters is the same either way.

On a gloomy day the partner's offer falls, and the falling number feels like a verdict. The discipline is a short sequence, done in order. First, ask whether anything happened to the business: a customer lost, a cost risen, a rival opened, a person gone. If not, this is mood. Second, find the zone. A gloomy quote that is still above your ceiling of 8.50 is in the middle zone, and the response is to ignore it. Only a quote below the ceiling, like day 8's 7.8 in the figure above, puts you in the zone where buying from him is worth considering.

"Consider" is the honest word. It means: check that your range still stands, then decide whether to take his offer at your ceiling or below it. It does not mean the low quote proves you right. Gloom can be wrong, and it can also be early, which is why the next card insists on the range being written before the quote.

If you have no written range when the quote arrives, the quote fills the gap. It is the only number in the room, so it quietly becomes your estimate of value, and from then on you are no longer using his price: you are obeying it. When he is elated your "value" rises with him, and when he is gloomy it falls with him. You end up buying after his good days and selling after his bad ones, which is the exact opposite of what the zones are for.

A written range breaks that pull because it was made before the quote and from different material: the owner earnings, the three views and the discount rate from Owner session 2. The sell floor works the same way. Halden's floor here is the high value of 15.8; some owners set it higher still, for the same reason a ceiling sits below the base. Either is a judgment, but it has to be your judgment, written in calm weather. The pull of the first number you see is the anchoring trap, and Owner session 6 takes it apart.

Nobody writes good rules on a day the partner is shouting. The rules that hold are the ones set on a quiet day, when no quote is pulling at you: your range, your ceiling, your sell floor, and one more line most people skip, which is what news would make you revisit the range. Write all four on one card and date it.

Then, when the quote arrives, your only job is to read the card. That is a smaller, steadier task than deciding from scratch. The card does not stop you changing your mind; it insists that you change it for a reason about the business, written down, and not because a number moved. If you cannot fill in the card for a business, that is Owner session 4's signal: it sits outside your edge, and Buffett's condition, understanding the business better than the partner does, is not met.

Ask two questions of any big move in the quote. Is there a new fact? Something about the customers (a builder leaves, or a large new one arrives), the costs (an importer raises prices, rent goes up), the rivals (a new showroom opens nearby, direct online ordering spreads) or the people (the cousin steps back, a key salesperson leaves). Would that fact change one of your inputs? The spend to stand still, the growth path in one of your three views, or how much weight you give the bear view.

If both answers are yes, you have a business change: revisit the range, on paper, using the input that moved, and only then look at the zones again. If there is no new fact, you have a mood change, however large the move: go straight to the zones. Most big moves fail the first question. A fact can also arrive on a quiet day with no move at all, and it still deserves a revisit; the quote is not the only messenger for news.