During the pandemic, airfares did strange things, and one case makes the whole method visible. A traveller searching for a flight from Larnaca to Heathrow on a given day was quoted, by the usual booking engine, a single fare of twenty-four thousand euros. The number is absurd on its face, and the ordinary response to an absurd number is to stay inside the system that produced it: try a different date, a different site, a different class — or give up. That response treats the booking engine’s output as a fact about the world. It is not. It is a fact about the booking engine.

Current Conditions

The Briefing in Five Lines
Two ways to thinkReasoning by analogy copies a solution that worked elsewhere: do what resembles the last success, or what everyone does. Reasoning from first principles breaks the problem down to what is demonstrably, irreducibly true — physical law, hard fact — and rebuilds from there. The first is the default; the second is the deliberate exception.
Analogy inherits hidden assumptionsCopying a solution copies its hidden constraints too. You import "this is how it's done" without checking whether the reasons still hold — or ever did. Most of the time harmless and efficient. Occasionally it means paying forty-eight times more than necessary for something whose real cost collapsed long ago.
The method is three movesIdentify the inherited assumptions — statements you treat as facts but are actually borrowed beliefs. Dig until you hit something you know rather than assume. Rebuild upward from that bedrock, ignoring how it has always been done. The skill is less in the rebuilding than in the digging.
It is expensive — use it sparinglyDeriving everything from scratch is slow; do it for every decision and you never leave the house. Analogy is not the foolish cousin of first principles — it is the rational default for the ninety-five percent of choices where the wheel needs no reinventing. The skill is recognising the few cases where digging pays.
The trap: false bedrockFirst-principles reasoning is only as good as your "first principles" are actually first. Stop digging too early — mistake an assumption for bedrock — and you build a rigorous-looking structure on soft ground, ending up more confidently wrong than someone who simply followed convention.

The Forty-Eight-to-One Move

The traveller did something else. Instead of asking the search engine for a better answer to its own question, they changed the question by dropping to a lower layer of reality. The booking site sells “a connection from Larnaca to London” as a single packaged unit with a single price. But that package is not the bedrock. The bedrock is physical: what aircraft actually left Larnaca that day? A glance at a live flight tracker answered it — one departure went to Zurich. From Zurich, onward flights to London were plentiful and cheap. Two tickets, booked separately as two real movements of metal rather than one marketed “route,” came to five hundred euros together. The same journey. A factor of forty-eight.

Look closely at what happened, because it is the entire method in miniature. The expensive price was not caused by physical scarcity. The seats existed; the aircraft flew; the journey was entirely possible at low cost. What was scarce — and therefore expensive — was the pre-packaged representation of the journey, the single bookable unit the system offered as if it were the only way the trip existed. The traveller separated the journey from its packaging: peeled away the layer the booking engine treats as reality, reached the layer underneath where actual planes fly actual routes, and reassembled the trip from those raw facts. That is reasoning from first principles, executed at an airport, with a real number attached.

The price was not scarcity of travel. It was scarcity of the packaging. The seats existed all along — only the convenient version of them was expensive.

Analogy Versus Bedrock

This is the difference between the two modes of thought, made concrete. Reasoning by analogy stays on the surface the system presents: “a flight is a thing you buy from a booking site, and its price is its price.” It is the right default almost always — you should not re-derive the airline industry every time you travel. But analogy carries an invisible cargo of assumptions, and the lethal one here was “the route the booking engine sells is the same thing as the journey I need to make.” First-principles thinking is the act of dropping below that assumption to the thing that is actually, physically true — metal leaving the ground — and noticing that the assumption and the reality had quietly come apart.

The famous version of this is the battery argument made by a certain electric-car founder. Convention held that battery packs cost around six hundred dollars per kilowatt-hour, always had, always would — a fact to be designed around. The first-principles question was different: what is a battery physically made of — cobalt, nickel, aluminium, carbon, some polymer — and what would those raw materials cost bought separately on the commodities market? The answer was a small fraction of the quoted price. The historical figure was not a physical floor; it was a convention no one had recently re-examined. Same structure as the flight: separate “expensive because it must physically be expensive” from “expensive because it has always been sold that way.” It is also the exact move that strips the “intrinsic value” objection off money down to what a currency actually is — the Larnaca traveller, the battery engineer, and the honest analyst of money all run the identical operation at wildly different scales.

The Three Moves, Named

Stripped to its mechanism, the method is three steps. First, surface the inherited assumptions — the propositions you are treating as facts that are really borrowed beliefs (“the route is the journey,” “packs cost six hundred a kilowatt-hour”). Second, dig until you reach something you genuinely know rather than assume — a physical law, a commodity price, a live list of departures. Third, rebuild from that bedrock without deference to how it has always been done. The center of gravity is the second step. Rebuilding is often easy once you are standing on real ground; the hard part, and the rare part, is digging down to ground that is actually solid rather than stopping at the first floor that feels firm.

Three-Layer Reading
What it saysFirst-principles thinking breaks a problem down to what is demonstrably true and rebuilds from there, rather than copying an existing solution by analogy. The 24,000-versus-500 flight is the method in one concrete move: drop below the packaged representation to the physical reality, and reassemble.
What it impliesMany "fixed" costs and constraints are not physical floors but unexamined conventions — packaging mistaken for reality. The leverage of the method comes from finding the cases where the assumed constraint and the actual constraint have silently diverged, and the price of that gap is being quietly paid.
What it means operationallyReserve the method for high-leverage decisions and entrenched fields where everyone shares one assumption — not for everyday choices where analogy is correct and far cheaper. And dig to genuine bedrock: the failure mode is stopping early and being confidently wrong, which is worse than having followed convention.

The Two Honest Limits

Because the method is powerful, it is oversold, and two limits keep it honest. The first is cost. Reasoning from scratch is slow and demanding, and analogy exists precisely because it is efficient and usually sufficient. The Larnaca move was brilliant because the arithmetic of effort favored it overwhelmingly — twenty minutes of research against twenty-three thousand euros — and because the trade-offs it introduced were acceptable: booking two separate tickets means carrying the missed-connection risk yourself, with no protected transfer if the first flight slips, possibly a second baggage handling, perhaps a transit visa. At a factor of forty-eight those risks are clearly worth bearing; at a factor of one-point-one they would not be. Knowing which case you are in — whether the leverage justifies the self-carried risk and the effort — is itself part of the skill. First principles is not a reflex to bypass every convention; it is the judgement to do so where the leverage is real.

The second limit is subtler and more dangerous: the method is only as sound as your first principles are actually first. The whole structure rests on having dug down to genuine bedrock — and the seductive failure is stopping at a layer that feels like bedrock but is itself still an assumption. Someone who halts the dig too early builds a rigorous, confident edifice on soft ground, and ends up more certain and more wrong than the person who simply trusted convention. The method can manufacture overconfidence: the feeling of having reasoned from the ground up, while having merely mistaken one’s own deeper assumptions for laws of nature. The corrective is humility about the floor — to keep asking, of each “first principle,” whether it is truly irreducible or just the deepest assumption you happened to stop at. Real bedrock can take being dug beneath and not move. If you have not tried to dig beneath it, you do not yet know it is bedrock.

What to Actually Take From This

First-principles thinking is the method quietly underneath most of this letter’s best work — and it is usually taught as a motivational slogan rather than the demanding, bounded discipline it actually is.

Separate the packaging from the reality. The core move is dropping below the layer a system presents as fact to the layer that is physically true — the route versus the metal that flies, the quoted price versus the commodity cost. Most “fixed” constraints are packaging. The leverage is in finding where the packaged version and the real version have come apart, and you are paying for the gap.

Use it where the leverage is real — analogy elsewhere. Deriving everything from scratch is expensive, and analogy is the correct, efficient default for almost everything. The skill is not thinking from first principles constantly; it is recognising the few high-stakes, entrenched-assumption cases where digging repays the cost — and accepting the self-carried risk that bypassing convention brings, when the factor justifies it.

Distrust your own bedrock. The method’s failure mode is stopping the dig too early and being confidently wrong on a foundation that was itself an assumption. A “first principle” you have never tried to dig beneath is not yet known to be one. Keep testing the floor — real bedrock survives the test, and the humility to keep checking is what separates insight from sophisticated self-deception.

Instrument Check — Worth Your Attention

Study — Aristotle on first principles, the original idea. The concept is ancient: Aristotle defined a first principle as the first basis from which a thing is known — a foundational truth not derived from anything more basic. Worth going to the source, because the modern startup version has flattened a rich philosophical idea into a productivity hack. The original is about the structure of knowledge itself, and it is sharper than its popularisations.

Read — on reasoning by analogy versus from fundamentals, the decision literature. Read the case for analogy as well as the case against it, because the honest position is not “always reason from first principles.” Analogy is how expertise actually compresses experience; the skill is knowing when it fails. The most useful framing treats the two not as smart versus dumb but as tools with different costs — and teaches the judgement of which to reach for.

Follow — the same move in other domains: The Outsourced Check and The Same Trade, Judged Twice. The first reclaims the individual check from consensus; the second strips the “intrinsic value” objection down to what money actually is. Each is the same act — refusing the packaged framing, digging to the layer that is genuinely true.

Flight Log — Dispatch From Altitude

The Larnaca story is, of course, an aviation story, but the deeper aviation parallel is not in the booking trick — it is in how pilots are trained to think when an instrument tells them something absurd. Early in training you learn a discipline that runs directly against instinct: do not trust a single reading that drives a major decision, and when a number looks impossible, do not just accept it and do not just dismiss it — cross-check it against an independent source that measures the same underlying reality by a different path.

Here is the shape of it. The airspeed indicator suddenly reads impossibly low on a takeoff roll; the altimeter shows you climbing when the aircraft feels level. The novice either believes the instrument and reacts to a phantom, or ignores it and reacts to nothing. The trained pilot does something else entirely: drops below the instrument to the reality it is supposed to represent. Airspeed is ultimately about air pressure in a tube — so is the tube blocked? Cross-check against ground speed, against the other pilot’s display, against pitch and power setting, against the standby instruments wired to a separate source. The skilled response to an absurd reading is to stop treating the gauge as the truth and go to the physical thing the gauge is a representation of.

That is exactly the Larnaca move, in a cockpit. The booking engine quoting twenty-four thousand euros is an instrument giving an absurd reading. The poor response is to believe it (pay, or abandon the trip) or to dismiss it without understanding (assume it is simply broken). The skilled response is to cross-check against the underlying reality the instrument is supposed to represent — the actual aircraft actually leaving the actual airport — using an independent source, the flight tracker, that measures the same world by a different path. In both cases the gauge is a representation, the representation has detached from the reality, and the discipline is to notice the gap and go to the thing itself.

And the cockpit knows the limit, too, the same one this issue insists on. You cross-check the readings that matter, not every reading on every flight — that would be paralysis, and aviation runs on trusting calibrated instruments the overwhelming majority of the time. The discipline is selective: most gauges, most of the time, are telling the truth and should simply be believed, because re-deriving reality on every glance is how you fly into the ground while staring at a tube. You reserve the deeper check for the reading that is both surprising and consequential. That is the whole craft, in the air and on the ground: trust the instruments by default, drop below them when the stakes and the strangeness are both high — and when you drop, go all the way to the metal, the pressure, the physical fact, and not to some intermediate gauge that is just another representation wearing the mask of bedrock.