Social media invites us to share our lives with friends. Back in February 2004, which Facebook launched, that seemed like a good and innocent thing. And it still can be for many users.

But there’s a dark side, too, one that’s emerged in the nearly two decades since social media’s inception. Some users like to share candid, unfiltered, authentic pics and posts. But for others, social media has become a world where you post the best, most-idealized version of yourself and your life. You might shoot a dozen selfies—or a hundred—to get that one perfect pose. Filters then further smooth out rough edges and light your portraits just right. And whenever you buy something cool, go somewhere cool or do something cool, well, you certainly don’t want to miss the opportunity to let all...