What’s Done Is Done
Aristotle saw it, economists named it, and almost nobody obeys it: what you have already paid is the same under every choice you have left, so it can never decide between them. AI delegates are about to obey it for us. That means we will finally have to say which parts of the past are promises.
- Option A = A’s future + what’s done
- Option B = B’s future + what’s done
- A − B = A’s future − B’s future
You are on page 312 of a 540-page novel you have disliked since page 80. You would never start this book tonight, and you are not going to stop, because you have already read 311 pages.
That reason feels like arithmetic. It is the opposite of arithmetic, and it is the most common way an ordinary person argues with the past.
The oldest rule in deciding
Everyone already believes the axiom underneath this. I have written about it for years under its proper name, the Immutable Past, and the short version is the one your grandmother used: what’s done is done. Nothing you do tonight will make those 311 pages unread, better spent or worse spent. Under every choice you could make from here, they will have been read, by you, in a month you will not get back.
Follow that one step further and you reach the first principle of every decision. If something is the same under every option, it cannot be the reason to pick one of them. Choosing is a subtraction, and a term that appears on both sides cancels. That is the whole figure at the top of this page.
The rule is old. Aristotle stated it in the Nicomachean Ethics: nobody deliberates about the past, only about what is still to come, because what has happened cannot not have happened. He borrowed a line from the tragedian Agathon to make the point. Of this alone even God is deprived, to make undone what has been done. Twenty-two centuries later the economist William Stanley Jevons said it in the language of trade: in commerce, bygones are forever bygones, and we start clear at each moment.
The same 311 pages are on both sides
Keep reading
- Already spent
- 311 pages
- Still to come
- 228 pages you do not enjoy
Close the book
- Already spent
- 311 pages
- Still to come
- The rest of tonight, back
Why knowing it does not help
Here is the strange part. Knowing the rule does almost nothing. In 1985 two psychologists at Ohio University, Hal Arkes and Catherine Blumer, sold season tickets to the university theater at three randomly assigned prices. Through the first half of the season, the people who had paid full price went to more plays than the people who got a discount, though every ticket opened the same doors. In their questionnaire studies, people who had taken economics did no better. The best explanation they found was plain. People do not want to appear wasteful.
Biologists call the same error the Concorde fallacy, after the supersonic jet two governments kept paying for long after it was clear it would never pay back. Committees have the error. Nations have it. Shakespeare gave the phrase itself to Lady Macbeth, which tells you how well it works as advice: she says “what’s done is done” in Act Three and is sleepwalking with it in Act Five.
So the error is not a lack of information. It is a feeling, and the feeling points backward. The sunk-cost error is a quiet attempt at time travel. Finishing the novel is a bid to turn a wasted month into an investment, to change what those 311 pages were by spending 228 more. It cannot work, because the axiom is the axiom. Finishing does not redeem the month. It only adds to it.
The Past is not a creditor
In my own framework the reason is structural. In the Reality Equation, the Actual arrives from the Immutable Past, and no one has any agency over the numerator. The past bears on the present by exactly one road: Actuals retrain prediction, so what happened changes what you expect next. That is its lawful job. It teaches. It has no second job collecting debts.
And here is the distinction everything below depends on. The Past is not history. The Past is complete and unreachable. History is the marks it left behind (receipts, scars, letters, contracts, memories), and every one of those marks is here, in the present, around you. A payment you made belongs to the Past. It is gone, and nothing can repay it. A promise you made is a different kind of object. It is a mark that is still here, and it names a condition on the present.
The Past cannot be repaid. History can be kept.
Two ledgers that humans keep mixing up
The Past · what you paid
The hours, the money, the pages, the years of a degree you would not choose again. Complete, unreachable, and identical under every option.
Use it as a lesson. Never as a reason.
History · what you promised
The vow, the handshake, the supplier you said you would stand by, the friend’s shop you said you would keep using. A mark that is still here.
Use it as a binding. It holds when the arithmetic says otherwise.
We mix these up in both directions. We honor what we paid as if it were a promise, so we finish bad novels, bad renovations and bad careers. Then, when the arithmetic turns against a real promise, we file it under sunk cost and call ourselves rational.
The first deciders without a flinch
Every decision-maker in history has been a creature that remembers paying: a person, a board, a parliament. Each one carried the flinch. That is about to change, and the change arrives quietly, through delegation. When you hand a matter to your AI and say you decide, you are handing it to a decider that can be built to read the past only as evidence. It can print what you have already spent beside every option, the same amount on every line, and let it cancel.
That is the good news, and most people will notice only that. The part most people will miss is that our sunk-cost error was doing a second job nobody wrote down. It was the crude glue of loyalty. Part of why people stay with the mechanic who has kept their building running for fourteen years, finish the marathon at mile twenty, or keep a struggling friend’s shop as their florist is the felt weight of everything already put in. Take away the flinch and you get a decider that ends bad things faster than any human ever has, and that can end good things just as fast, for the same reason.
So the delegate does not remove the work of the past. It moves it. Someone now has to say, out loud and in writing, which marks are promises. That someone is you.
Your delegate’s morning report says it ended the kitchen contract seven months in, because finishing with another crew costs less than finishing with this one, and it withdrew you from the course you stopped attending in March. The last line says it moved your building’s service contract away from Ray (fourteen years, and the Sunday in August he drove over when the compressor died) to a cheaper firm, and you open the mandate and type one sentence: Ray is a promise.
Five predictions
Your delegate will quit things for you.
The first large effect of AI acting on our behalf will be a wave of endings: renovations, courses, contracts and half-built plans kept alive only by how far they had come. Each one will sting for a day. The relief will last longer.
“We’ve already put in…” stops working in rooms.
When every recommendation arrives with the amount already spent printed beside every option, identical on each line, the sentence that has kept failing projects alive in every boardroom loses its audience. People will have to give the real reason, or stop.
Loyalty gets written down.
A delegate that cannot feel the money you spent also cannot feel fourteen years. So people will start writing their promises into the mandate: this supplier, this cause, this friend’s business, through a bad year. The vow comes back, as configuration.
Finishing becomes a decision.
Fewer things will be finished out of guilt. The things that do get finished will be finished because someone decided the finishing itself was the promise. Perseverance stops being an accident of what was spent and becomes something you said.
The past gets read for its lessons, harder than ever.
What you spent is still information. It says your estimate was wrong, that this kind of work runs long, that you overrate your own patience. Delegates will use that relentlessly, and your next forecast will be better because your last one failed. The past keeps its one lawful job. It teaches.
Where I stand
I ask every class I teach the same question: can you change the past? I have never had a different answer. Nobody needs to be persuaded. And still every one of us, me included, has walked further toward something we would not choose today because of how far we had already walked. We believe the axiom. We do not yet obey it.
When I tell my own AI you decide, this is the deal I want: the past as evidence, never as debt, plus a short list, in my own words, of the marks that are promises. I wrote about the mandate in My AI Delegate and about what never to hand off in The Great Matters. This piece sits underneath both.
The claim ledger
- Already true
- The principle is not in dispute. Aristotle said it, Jevons said it, every first course in economics teaches it, and the experiments show that the teaching does not cure the habit. AI is already being handed small matters with the authority to decide them.
- What has to happen
- Delegates have to be given real authority to end things, not just to recommend endings. They have to be built to set what was spent beside every option instead of inheriting our flinch. And people have to accept a recommendation to walk away from something they paid for.
- Where I am probably wrong
- Two places. Models learn from our writing, and our writing is soaked in “we’ve come this far,” so the delegate may inherit the flinch instead of losing it. Or a well-built delegate may honor loyalty on its own, because breaking faith costs future trust; then the two ledgers collapse into one calculation and nobody ever has to type “Ray is a promise.” If by 2030 people who delegate still finish doomed projects at the same rate as people who do not, the first prediction is wrong, and the error lives deeper in us than I think.
Back to page 312. Close the book. The 311 pages are done. They were done the moment you turned them, and they sit on both sides of every choice you have left, so they cannot choose for you. What is not on both sides is the rest of tonight.
What’s done is done. It is not waiting for you to finish.