I handed an agent "do all of this," then got up to make coffee.
I came back and opened the diff: forty files. It changed things I didn't even remember existed. And somewhere in the middle, one wrong decision had quietly dragged a dozen later steps into building on top of it. I sat there staring at the giant diff, knowing one thing for sure: there's no reviewing this. Nothing to do but revert it all.
That's the lesson I keep relearning: one giant turn is exactly where an agent drifts furthest.
01Why a longer turn drifts further
Each step the agent takes builds on the one before. If step two is slightly off, then steps three, four, and five all build on that wrong step — consistently. So each step looks reasonable on its own; only the whole is wrong. By the time you can see the full picture, it's gone too far to fix locally.
The way to stop it is so simple it's easy to skip: don't let it run in one breath.
02How big a stage should be
A good stage meets two conditions: reviewable in one sitting (you look at the diff and actually understand it, not skim to feel done), and throw-away-able cleanly if it breaks, without dragging another stage down.
The best sizing question: "If this stage is completely wrong, how much do I lose?" Answer "a morning" — good size. Answer "three days" — cut smaller.
03A checkpoint is a save point
Think of a game with saves. You don't blast through the whole hard level and only then save — you save after each stretch you clear. A big structural change, split into the classic three stages: prepare → switch → clean up. Broke at "switch"? You still have the save after "prepare" to fall back to. Without stages, you have exactly one save — before you started — which means redoing it from zero.
04And a bonus you didn't ask for
There's an underrated perk: stages give you the right to change your mind cheaply. After stage one, you realize the direction isn't as good as it sounded — you stop, cheaply. One giant turn leaves you no such door; by the time you see it, the budget's spent.
Staging sounds like slowing down. It's actually the only way I know to move fast without doing the work twice.