What does it mean that other people are calibration instruments?

Other perspectives correct for your systematic blind spots.

Example: A startup CTO is convinced her team communicates well. She has never received a complaint. She interprets silence as agreement. Then she runs a structured peer feedback round — anonymous, specific, scored on a five-point scale. The results reveal that three of her five direct reports find her interruptions in technical discussions demoralizing, that her habit of restating others' ideas in her own language is perceived as credit-taking, and that her open-door policy feels performative because she checks her phone during every conversation. None of this was visible to her. Not because she was careless, but because the same perceptual system that produced the behaviors could not detect the behaviors. Her team became the calibration instrument her introspection could never be.

Try this: Identify three people who observe you in different contexts — a colleague, a friend, and a family member. Ask each one the same three questions: (1) What is something I do that I probably do not realize I do? (2) What is something I seem to believe about myself that does not match what you observe? (3) When have you seen me be most wrong about something while being most confident? Write down their answers verbatim — do not paraphrase, reinterpret, or soften. Compare across all three respondents. Any overlap is high-signal: it identifies a blind spot that multiple independent observers have detected and that your own introspection has missed.