This document discusses the state of characterization of the eukaryotic proteome. It notes that as of 2019, around 20% of proteins in fission yeast and humans are still classified as having unknown biological processes. While the number of known or inferred protein roles has increased since 1992, progress in characterizing unknowns has been slow. Many recently characterized proteins in fission yeast are involved in non-core functions like environmental response, aging, and damage accumulation. The document calls for more research on these unknown and less studied proteins that are "hidden in plain sight" within the eukaryotic proteome.