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

The remark reframes “expertise” as the hard-won result of trial, error, and correction rather than innate brilliance or mere credentialing. By stressing “all the mistakes” and “a very narrow field,” it highlights two features of real mastery: depth (intimate familiarity with the ways things fail) and specialization (competence is bounded, not universal). The line also carries a pragmatic, scientific ethos often associated with twentieth-century physics: progress comes from confronting error, refining models, and learning the limits of one’s assumptions. As a maxim, it encourages intellectual humility—experts know more partly because they have been wrong more often, and in more instructive ways, than novices.

“An expert is a man who has made all the mistakes which can be made, in a very narrow field.”
“An expert is someone who has made all the mistakes that are possible in a very narrow field.”