It's sad when someone you know becomes someone you knew.

The line captures a common modern grief: relationships can end not only through death but through drift, rupture, or reinvention. Its power comes from the grammatical pivot—“know” (present intimacy) to “knew” (past-tense distance)—which compresses an entire story of estrangement into a single word change. It suggests mourning for a living person: the loss of shared context, trust, or mutual recognition. The quote also implies how identity is relational; when someone changes—or when circumstances change—you may lose access to the version of them you were close to, leaving memory to replace connection.