The test of intelligence [is] not how much we know how to do, but how we behave when we don’t know what to do. Similarly, any situation, any activity, that puts before us real problems, that we have to solve for ourselves, problems for which there are no answers in any book, sharpens our intelligence.

John Holt (1923-1985) American author and educator

How Children Learn, “Art, Math, and Other Things” (1967)