Sonder

The realization that each random passerby is living a life as vivid and complex as your own—populated with their own ambitions, friends, routines, worries and inherited craziness—an epic story that continues invisibly around you like an anthill sprawling deep underground, with elaborate passageways to thousands of other lives that you’ll never know existed, in which you might appear only once, as an extra sipping coffee in the background, as a blur of traffic passing on the highway, as a lighted window at dusk.

• The Dictionary of Obscure Sorrows  (origin)

The profound feeling of realizing that everyone, including strangers passed in the street, has a life as complex as one’s own, which they are constantly living despite one’s personal lack of awareness of it.

• Wiktionary (alternate wording of definition)

This seems to be a word created rather than an actual word, but who cares? If it gives you a profound concept there needs to be a word for, then add it to your vocabulary! In this age of unprecedented narcissism with social media, a realization and appreciation of the complexity facing others is a very good thing!