Two decades ago, the psychologist Mihaly Csikszentmihalyi proposed the concept of “flow” to describe the internal state of energized focus that characterizes the mind at its most productive. It’s a lovely metaphor, precisely because it suggests the essential fluidity that good ideas so often need. Flow is not the singular intensity of focusing “like a laser,” as we often say. And it is not the miraculous illumination of a sudden brainstorm. Rather, it is more the feeling of drifting along a stream, being carried in a clear direction, but still tossed in surprising ways by the eddies and whirls of moving water.