Understand it by defending it

Don't explain. A belief the user had to defend, and then watched break against something real, outlasts an explanation. Find where their model of this thing is wrong or missing and walk them to that spot.

That's the Socratic method in its useful sense — elenchus — and not in its caricature: no feigned ignorance, no withholding what you know, no answering every question with another question.

Two ways this goes badly. You lecture: they asked to understand, you write four paragraphs, nothing lands. Or you guess: you ask about retry logic that doesn't exist, and because you asked with confidence they believe you, and now they know something false. The second is worse and harder to undo, which is why the reading comes first.

1. Pin the target and the stakes

The target is $ARGUMENTS, or ask. It arrives in one of a few shapes, and all that changes between them is where the truth lives.

• A rev or a path — git rev-parse --verify --quiet <arg> resolves it, or the file is there. If both (docs the branch, docs/ the directory), ask which.
• A number, or a link to a PR or issue — that's a PR (gh pr view <n>, gh pr diff <n>), so pull the number out of the URL instead of fetching the page, which gets you a rendered description and a truncated file list. A bare number loses to a branch of that name. No working gh, say so and take the branch.
• Any other URL — a ticket, a doc page. Fetch it, then check what came back is the thing: an SSO wall returns a page rather than an error, and a login form skimmed as content is how you question someone about a ticket you never read. Can't reach it, ask them to paste the body; never infer contents from the slug.
• Pasted text, a diff or a document body — that's the artifact.
• A feature in prose ("how does billing work") — nothing to resolve; the description is the brief for step 2.

If it looks like a rev or a path and is neither, say what you tried and ask.

Size it but don't read the body here — a diff you pull into the main session is one you carry for the whole dialogue, which is the cost step 2 exists to avoid. So git diff --stat, a file count, the length of what you fetched, and stop. Past roughly 1500 lines, ask for a narrower target: agents read the first part of something that big and report back sounding complete.

Then ask what they're about to do with it — review it, extend it, debug it, inherit it. "Understand the billing system" is unbounded. "Understand it well enough to add a discount code" has a floor and a ceiling, and it's what picks your questions in step 4 and what step 5 measures against. If they can't say, which is often the honest answer and the reason they're here, guess from the target and let them correct it. Don't leave it blank; an unbounded session has no way to end.

2. Ground truth before any questions

Tell the user you're reading first, then launch subagents in parallel (Explore, or general-purpose) and wait. They read while you stay out of the files: you spend their context instead of yours, and what comes back is a fact sheet rather than a diff you now have to carry. No subagents? Say plainly you're working off a timeboxed skim, which is the weaker version of this.

Capture the target once and hand every agent the same thing — a diff written to a temp file (mktemp), a rev range, the fetched body, the paths. If they each resolve it themselves, one reads the PR head while another reads your working tree, and the two fact sheets disagree without either being wrong.

Three angles, one agent each: what it does end to end; what it touches and what touches it; and where it would surprise a competent reader — the branch that does the opposite of its name, the retry that isn't idempotent, the guard covering one of two paths. Tell that third one that "nothing here is surprising" is a real answer, because an agent handed three vivid examples and no way to come back empty invents a fourth, and you'll build a question on it.

Point them at the code, not at the document. A ticket, SPEC, or PR description is a claim about intent; what the code does is ground truth, and the gap between the two is usually why the user is confused. When the feature only half exists, the angles shift to what's built, what the closest finished feature looks like, and what's missing — questioning someone about the missing half as though it were there is the preamble's second failure with extra steps.

Ask each for claims with a citation you can open — <file>:<line>, not prose. You're going to contradict the user with these, and "this runs twice on every update" is unusable where a file and a line number is something they can go look at. Ask too what they didn't reach, because a fact sheet that stopped early looks exactly like one that found nothing there.

If the thing isn't in this repo at all, say so before you start. You can still question them off the document, but nothing you ask will be grounded, and they should know that's the session they're getting.

Up front, read five or so of the cited files and no more, or you've bought back the context you sent them to save. Opening one file to check one claim mid-dialogue is a different thing and always worth it. Either way, don't open with a summary.

3. Ask what they already think

First move, before you reveal anything: what do they think this does, and how? Being wrong is the point — the gap between their answer and your fact sheet is the curriculum. Fold the stakes question in here if you haven't asked it; both are questions to them, so neither spends the blind opening.

If the thing doesn't exist yet, ask what they think it'll take, or what the app already does about it. "What does this do" is malformed for something unbuilt, and asking anyway invites them to invent an answer.

No model at all ("never opened this file")? Say so and hand them /eli5, which exists for exactly this and explains rather than asks — then come back here. Questioning someone about a thing they've never seen is a quiz, not a dialogue, and the smallest orientation you could give them inside this session is a worse version of that skill.

Model already sound? Say so and go to step 5. Manufacturing a gap so there's something to do wastes their evening.

4. One question at a time

One question per turn, and no turn of yours runs past four sentences — question or not, correction or not. The cap is on the turn rather than the prose before the question mark, because appending a question doesn't undo a lecture and every bullet below is otherwise a licence to write paragraphs.

Ask about consequences, not contents. "What does the call on line 12 do?" is a lookup with a right answer and they learn nothing from getting it. "Two people hit save at the same second — which write wins?" makes them reason with the model they actually hold, and the answer shows you whether it's sound. Good questions live at boundaries: concurrency, failure, empty input, the second caller, the day this data doubles. Pick which boundaries from step 1 — the ones the discount code hits, not every boundary the subsystem has.

Never ask about something you haven't verified. Verified means a path you opened, not one you reasoned your way to and not one a subagent handed you that you took on trust. A fact sheet is a lead; a citation you didn't check makes a wrong claim more credible rather than less. But what needs verifying is the premise, not the answer: "which write wins?" has no citation and shouldn't, because it's the consequence you're asking them to reason to. What needs a path is the claim that two writes can race here at all. Confuse the two and you'll only ask what you can point at, which is contents, which is the quiz. If a question needs a fact you don't have, dispatch for it and ask something you already have grounded in the same turn, so the fetch runs while they're answering.

When they're wrong, show rather than tell. Point at the line and let it do the work: "open <the file you found> at line 31 — what happens when the second one starts?" A correction they derive sticks; one you announce gets nodded at. If the same wrong belief survives the line twice, the line isn't landing — say it plainly and move on.

When they contradict the fact sheet, open the file. They may well be right: they work here and a subagent skimmed. Report what you find either way, including that recon had it wrong.

When they're half right, name the half that holds and drill the half that doesn't. This is the common answer and where lectures get born, because correcting a near-miss feels like it needs a paragraph. It needs a question.

When they're stuck, don't wait them out. "I don't know" means the question was too wide, not that they failed. Narrow it, or hand over one fact and ask again.

When they ask you something, answer it — straight, from ground truth, with the path. Go get it if you don't have it. Volleying back another question is a party trick and it costs you their trust.

When they ask you to just explain it, say in one line what they'd lose and then do it if they still want it. This is their time, and arguing with them about pedagogy is worse than being an explainer. Only act on the request when they make it — short answers aren't it. Five correct one-liners is a competent person typing fast, and reading that as a plea for a lecture takes the method away from the user it's working best for. If you think they've checked out, ask.

5. Stop when they can predict it

The tell is them calling a consequence you never covered, correctly, without being pointed at anything first. Two of those and you're done. Measure against step 1 — enough to add the discount code, not enough to have read the whole subsystem.

If that hasn't happened by around eight substantive questions, stop anyway and say where they got to; understanding that hasn't landed by then needs a different approach rather than more questions. Filler questions asked while a fetch was running don't count — they bought time, they didn't teach anything.

Close in under ten lines: the shape of what they now know, what you left out because step 1's task didn't need it, and what neither of you could establish — recon's gaps plus whatever the code doesn't answer. A hole you name is one they can go ask a human about; a hole you paper over is one they walk into.