Be Conservative in What You Send, Liberal in What You Receive

A one-sheet on posture toward the people around you The principle, and its known failure Jon Postel wrote it for computers talking to each other: send strictly correct output, accept anything you can reasonably interpret. It let a fragile early internet work despite everyone’s software being slightly wrong. Engineers later turned against it. Broken implementations survived because everyone quietly worked around them. Malformed input became an attack surface. The real standard drifted from the written spec toward “whatever people actually send.” Later standards walked it back. Both halves transfer, but not symmetrically. In protocols, liberal acceptance causes drift — the spec rots slowly. In people, it causes adaptation — the other party notices and adjusts. Which is the thing to hold onto: charity here isn’t only a private virtue. It’s an intervention in a system that reacts to it. Three tiers, not two Form — be liberal. The blunt email. The typo. The question asked badly. The friend…