In the 1970s, the Japanese roboticist Masahiro Mori introduced the concept of the “uncanny valley.” The valley effect occurs, he believed, when an artificial form is almost—but not quite—authentic enough to feel like the reality it is emulating. People experience an unpleasant disconnect when viewing such objects, and they become fearful and repelled. Technical perfection adds to, rather than subtracts from, the feeling; a perfect robotic face can leave the viewer disquieted and nauseated. Imperfections are sometimes added to mitigate the effect.

In real life, imperfections may be what we prize most dearly in those we find beautiful. They are not merely tolerated as necessary but celebrated and fantasized about in themselves. Flaws give us a chink through which to view great bea...