The word “solipsism” is cobbled together from a few Latin words: “solus” (“alone”), “ipse” (“self”), and the “-ism” suffix, which forms nouns. German philosophers combined these parts in the mid-19th century for a theory that one’s own mind is all that exists — anything outside of it cannot be known. As time passed, the name for the philosophical belief was adopted into more casual usage to describe the general quality of being self-centered. However, solipsism isn’t an average preoccupation with self; it’s an extreme form of selfishness.