Feedback is the ingredient, and it must arrive quickly

Domains where the world answers back promptly and honestly grow real experts, and the rest struggle.

If expertise is tuning, something has to do the tuning, and that something is feedback. The domains that reliably produce genuine skill share a structure: you make a judgement, the world responds, and the response arrives soon enough and clearly enough to be attached to the judgement that caused it. Repeat this a few thousand times and a person's intuitions become an instrument. They will often be unable to explain how they know, which is normal and not a red flag. The knowledge lives in the calibration, not in the explanation.

Notice what that structure requires. The response must be timely, because a correction that arrives years later cannot be linked to the specific choice that earned it. It must be unambiguous, because if the outcome can be read several ways the practitioner will read it favourably, as everyone does. And it must be frequent, because rare feedback means a lifetime's career might contain only a handful of genuine corrections, which is not enough repetitions to tune anything at all.

Where those conditions hold, be reasonably generous. Confidence built on thousands of quick corrections has earned something, and treating it as mere opinion is its own kind of error. Where they do not hold, the same outward signs of expertise can be present with nothing underneath: the vocabulary, the calm, the years of service, the sense of having seen it all before. The person is not lying. They have simply never been in a position to find out whether their judgement is any good, and neither have you.