An expert is a man who has made all the mistakes which can be made in a very narrow field.

Bohr’s remark reframes “expertise” as the hard-won product of trial, error, and accumulated correction rather than innate brilliance or mere credentialing. In a “very narrow field,” progress often comes from repeatedly confronting the same limited set of possibilities until one has encountered—and learned to avoid—nearly every failure mode. The quote also carries a note of scientific humility: even the most accomplished specialist is, in effect, someone who has been wrong many times in a bounded domain and has refined judgment through those mistakes. It implicitly values experience, iteration, and intellectual honesty over authority or certainty.

An expert is a person who has made all the mistakes that can be made in a very narrow field.
An expert is someone who has made all the mistakes which can be made in a very narrow field.
An expert is a man who has made all the mistakes that can be made in a very narrow field.