“Being a mathematician is no more definable as “knowing” a set of of mathematical facts than being a poet is definable as knowing a set of linguistic facts. Some modern math ed reformers will give this statement a too easy assent with the comment: Yes, they must understand, not merely know. But this misses the capital point that being a mathematician, again like being a poet, or a composer or an engineer, means doing, rather than knowing or understanding.”
Papert, S. (1972). “Teaching children to be mathematicians versus teaching about mathematics.” International Journal of Mathematical Education in Science and Technology 3(3): 249-262.