21st century society considers me extremely useful, because I happen to be very good at solving certain kinds of puzzle. Medieval society would consider me practically useless, because I'm frail, clumsy and almost blind. My usefulness now and my uselessness then is almost entirely a fluke of genetics.

Valuing people for their utility is incredibly dangerous, because it logically invites us to devalue people for their lack of utility. My community is full of broad-shouldered, hard-working men who became economically useless when the coal mine closed. They're not worse than me, they were just born a few decades too late. They deserve every comfort that society affords me, but the fallacy of meritocracy has provided society with a plausible excuse to neglect them.