Game Theory · Diagnosis Clinic C · after Lesson 11 · the whole toolkit · ← Lesson 11

Which lens, out of all eleven?

Clinic A handed you four candidate lenses. Clinic B handed you four more. This one hands you nothing — eleven lenses, six live cases, and the discipline to pick cold is the entire game now.

~15 min · after Lessons 01–11 Skill: diagnosing across the whole toolkit Format: unlabeled cases, no hints

WHY THIS EXISTSYou now own eleven lenses. The last skill is choosing among them.

Run the roll call: L01 dominance test — wins no matter what they do. L02 value the matrix — model their objective, not yours. L03 iterated dominance — cross off what a rational opponent would never do. L04 best response & Nash — the stable pair when nobody has a dominant move. L05 coordination & focal points — when the fight is agreeing, not winning. L06 sequential games & backward induction — someone moves first, the other reacts. L07 commitment & credibility — giving up your own options on purpose. L08 repeated games — the shadow of the future and tit-for-tat. L09 signaling & screening — one side knows more, and either proves it or designs a menu. L10 bargaining & BATNA/ZOPA — your power is your walk-away. L11 mechanism design — you don't play the game, you write its rules.

Below are six situations from your real world, stripped of their labels, drawn from the same live decisions in DECISIONS.md. Three lean on the newest tools. Two are cumulative — the correct lens could be any of the eleven, and the wrong answers on offer are the ones people reach for out of habit. One is a trap: a shape that looks like a deal to be split but isn't one at all. Diagnose first. Solving is the easy part once you've named the shape correctly.

THE CASESSix unlabeled decisions

Case 1

Your particular consult price sits well above what three other clinics in Porto Alegre charge — and instead of just asserting quality, you publish your real GTR and complication rates on your site for anyone to check before they book.

Which lens?

Signaling (L09). You're the informed side — you know your true skill, the patient doesn't. Publishing real outcomes data is costly precisely because a mediocre surgeon can't fake good numbers; that asymmetric cost (Spence's single-crossing condition) is what makes it a credible signal rather than a banner that just claims "trusted care." Screening would be the reverse move — you designing a menu that makes the other side reveal itself. Here you're the one being evaluated, so you signal.
Case 2

A health-plan administrator offers to add your practice to their network — but before naming a number, you first tally what you already bill self-pay for that same volume, because that's what you'd keep doing if this negotiation goes nowhere.

Which lens?

Bargaining & BATNA/ZOPA (L10). Naming your outside option first — what you'd keep earning self-pay if talks fail — is exactly the BATNA discipline: it sets your floor before you say a number out loud. Once you also estimate the payer's ceiling (their cost of routing volume to a competing practice), the gap between the two is the surplus actually being negotiated. Modelling their objective (L02) is a real input here, but it's a step inside the bargaining frame, not the frame itself.
Case 3

You pay referring physicians a flat fee per patient they send, no matter whether that patient shows up for a consult — and lately the referrals have skewed toward padded, low-acuity leads chasing the fee rather than genuine cases.

Which lens fixes this?

Mechanism design (L11). Referrers are gaming a badly-built rule, not behaving badly as people — the fix is to pay on consultation completed, not on lead sent, so that sending a genuine, qualified patient becomes each referrer's own best move. That's incentive compatibility: you don't police them, you redesign the game so honest behavior is the self-interested behavior. Punishing them round after round (L08) treats a mechanism problem as if it were a relationship problem — the mechanism is what's broken.
Case 4 · cumulative

You publish, in writing, on the SlideCraft pricing page: Expert-tier subscribers keep their $59 rate for life, even after list price rises — and you deliberately make it a public promise, not a quiet internal policy, so you can't walk it back later without visibly breaking your word.

Which lens, now that all eleven are in play?

Commitment & credibility (L07). The move isn't finding a stable outcome (Nash) or accumulating trust round by round (repeated games) — it's deliberately destroying your own future flexibility, the quiet-policy-reversal option, so the promise becomes credible today. A public, hard-to-reverse commitment is the whole mechanism: subscribers believe "$59 for life" precisely because you've made backing out visibly costly to yourself, not because they trust your goodwill.
Case 5 · cumulative

You raise your Google Ads bid on your shared keyword and leave it running, visible, at the top of the results all month — before the rival clinic sets its own bid for the period — counting on them anchoring their number off whatever they see sitting above them.

Which lens?

Sequential game — a game tree (L06). You moved first and made your move observable on purpose, expecting the rival to react to what they see rather than choose blind. It isn't a simultaneous matrix — there's no dominant bid here, your best move genuinely depends on theirs — and it isn't about punishment across many rounds. It's a first-mover play: figure out what a rational responder does once they've seen your bid, then work backward to what you should actually post.
Case 6 · the trap

A prospective device sponsor for the skull-base course tells you, plainly, that their entire regional marketing line for this quarter is capped at R$12,000 — full stop, no exceptions. You already hold a signed offer from another sponsor for R$18,000.

Which lens?

No ZOPA (L10, the trap). Your floor — R$18k, your existing signed offer — sits above their hard ceiling of R$12k. There is no price that beats both outside options, so the zone of possible agreement is empty. This isn't a deal to work harder at splitting; it's a bargaining shape to recognise and exit. Threatening to walk (L07) only does work when walking is a bluff you might not need — here walking isn't a threat at all, it's simply the correct move: take the R$18k offer.

THE TELLHow to tell them apart in five seconds

If you catch yourself thinking…Reach for
"Wait — which of the first eight tells was this again?"Clinics A (L01–04) & B (L05–08) hold those fingerprints — this page only adds L09–11
"I know something they don't — words alone won't prove it"Signaling (L09) — take the costly, hard-to-fake action
"They know something I don't — I need them to sort themselves"Screening (L09) — design the menu, let them self-select
"The first question isn't what I want — it's what I get if we don't agree"Bargaining & BATNA/ZOPA (L10) — find floor, ceiling, surplus
"My floor sits above their ceiling — no price beats both outside options"No ZOPA (L10) — take your BATNA and walk
"I'm not really a player here — I get to write the rules"Mechanism design (L11) — redesign so honest is each player's best move
The clinic's one idea, one last time

Eleven lenses are useless if you can't tell, cold, which one a live situation needs. The tool was never the hard part — recognising the shape before you reach for anything is. That recognition is the actual course.

YOUR REPDiagnose a real one, cold — and run it

Do this before you next solve anything. Open DECISIONS.md, pick a row from Live Now or Recurring — the payer matrix, the sponsorship ask, the referral incentive redesign, whichever is most live this week. Before reaching for any matrix, write one line: which of the eleven lenses is it? Not a category from this page — from the whole arc.

Then say why in a sentence, solve it, act on it, and move the row to Resolved once it plays out. Write the REVIEW-*.md — predicted outcome vs. actual, and what the matrix got wrong. That back-half honesty is what turns eleven quiz lenses into one working instinct.

The gate: the win was never six correct answers on this page — it's catching yourself, on a live decision, reaching for the right lens before anyone hands you a label. Log the first real one you diagnose correctly, cold.