Bohr presents expertise as the accumulated result of making mistakes and learning from them. Rather than defining an expert as someone who never fails, he suggests that expertise develops through direct experience of what can go wrong. The reference to a “very narrow field” also highlights the specialised nature of knowledge: even considerable expertise may apply to only a limited area.

The observation reflects an apparent paradox in learning. A mistake may seem obvious and easily avoidable once it has happened, yet recognising the danger beforehand can be surprisingly difficult. Direct experience often makes a lesson more memorable than abstract instruction, helping people identify problems they might otherwise overlook.

The quotation also suggests that repeated practice can gradually reduce errors. If mistakes are recognised, understood and avoided in future, experience can steadily improve judgement and performance. However, progress depends on learning from errors rather than merely accumulating them. Expertise therefore involves both practical experience and the ability to reflect on its lessons.

Common variation

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