What is definition of sonder?

Sonder is a word coined by John Koenig, and it refers to the realization that each passerby has a life as complex as one's own, complete with their own ambitions, worries, and moments of joy and despair. It is a feeling of empathy and understanding for someone else's experiences, a recognition that everyone has a unique story that informs their perspective on the world and their place in it. The word has gained popularity in recent years and has been used in literature, social media, and pop culture to express a deep appreciation for the diversity and complexity of human life.