Field Note · 3 June 2026
When you work on your own, the thing you miss most is a second pair of eyes.
Trades have known this forever. Carpenters say measure twice, cut once — because once you’ve cut the board, you can’t un-cut it. Banks and pilots call it the four-eyes principle: nothing important ships on one person’s say-so, two people check it, always. The whole point is to catch the mistake while you still can, because some mistakes don’t let you take them back.
Work alone and that second person doesn’t exist. So last week, hardening a tool before it went anywhere near real users, I built one.
I didn’t ask one AI to check my work — one is no good for this, it mostly agrees with you and it shares your blind spots besides. I gave the exact same job to two different ones at once — OpenAI’s Codex and Google’s Gemini, each working on its own, with Claude running the pass — and then watched where they disagreed.
The agreement was the easy part: five things they both flagged, which is about as close to “this is definitely a problem” as you get without a human in the room. The catch was in the disagreement. One of them, on its own, spotted a mistake the other two walked straight past — a setting that would have quietly logged my paying members out, for no reason they could see, with nothing on my end to tell me it was happening. The kind of thing you don’t find out about until someone emails to ask why they keep getting kicked out.
That’s measure twice, cut once. The second pair of eyes caught the bad cut before it shipped.
One warning, because this is where it goes wrong: don’t hand the whole thing over. That mistake was dangerous precisely because it failed silently — no error, no alarm, just a confident wrong answer. If a second AI buys you a bit of confidence, spend it putting your own checks back in, not switching your brain off.
And it isn’t only for code. Anything you’re about to commit to that you can’t easily take back, and can’t fully check on your own — the contract clause, the pricing change, the email you can’t unsend — is a candidate for two independent opinions and a hard look at where they don’t line up. The disagreement is the part worth your attention.
Some nights that second look is worth the trouble. Some nights it isn’t — and the right answer is to shut the laptop and go for a walk.
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— Jim