The realization that everyone around you has a life outside of yours, complete with their own thoughts, feelings, and emotions. You could potentially be just a passing figure on the street to them.
Sam and I were sondering down the street one day.
Briefly, "the realization that each random passerby is living a life as vivid and complex as your own." Originally from the Dictionary of Obscure Sorrows, which has a lot more beautiful neologism definitions like this you might enjoy.
I felt deep sonder thinking about the all the people who looked up this word along with me.
n. Pseudophilosophical guff memetically spread by the tumblr blog "The Dictionary of Obscure Sorrows". No academic grounding whatsoever, can be figured out through common sense.
I just had a sonder.
A what? Stop talking shit!