Eve Fairbanks, a writer who lives in Johannesburg, is at work on a book about South Africa.

A few weeks ago, I saw a jazz bassist play. I’d seen him before in a different venue, with a different, smaller audience. That crowd sat stony-faced as he coaxed his beats out of the belly of the instrument; he tried laughing and howling and crooning as he played, but we remained unmoved.

This recent night, though, he had younger, looser fans, who screamed as he screamed, playfully batted back his smiles like tennis balls, swiveled and danced between tables. And they brought forth a completely different man.

In front of the dead crowd, the bassist had seemed old, low-energy. His eyes were visibly cloudy with cataracts, his brow sagged, his fingers slowed as the night wore on. Yesterday evening, though, he was 15 years younger, lithe, jumpy, radiating grins.

He seemed like another person entirely, and he was. How thoroughly we are made by the intercourse we have with the people around us! We love to think, in contemporary life, that we are best and fullest on our own. “You have to be whole before you can be anyone’s half,” the reality-TV star Toya Wright said. Our favorite millennial self-help pastimes, yoga and meditation, propose that we have some singular essence that can be discovered and distilled without other people.

When I hear people say we are forged in solitude, or that we can even “find ourselves,” I suspect this is wishful thinking, born out of the fear we inevitably feel when we realize how much we are raw clay sculpted by hands we cannot fully control. John Lennon was a function of Paul. Yeats of Maud Gonne. Lincoln of the slaves he witnessed boating down the Mississippi and then of Joshua Speed, his best friend and lifelong correspondent. I’m the creation of those who have loved and hated me, in equal measure.

If we know this, we also must face the fact that what we do in our lives is not for us alone. It might not even mainly be for us. How would we live if we understood we may create the people we encounter even more than we create ourselves?