YOU MAY NEVER HAVE READ "Walden," but you're probably familiar with the premise: a guy with an ax builds a cabin in the woods and lives there for two years to tune out the inessential and discover himself. When Henry David Thoreau began his grand experiment, in 1845, he was about to turn 28—the age of a typical Instagram user today. Thoreau lived with his parents right before his move. During his sojourn, he returned home to do laundry.

Thoreau's circumstances, in other words, weren't so different from those...