"Onism" is a term coined by John Koenig in The Dictionary of Obscure Sorrows, used to describe a frustration or sadness derived from the awareness of how little of the world we will experience in our lives.

It comes from thinking about unfulfilled experiences, and extends to thoughts about how small and finite we are relative to the realm of all possible experiences/outcomes. As someone who once thought he would have a lifelong career as a painter, this idea resonates with me deeply, ...