The phrase "不为人知" is formed through a classical Chinese grammatical structure where the four characters combine to create a passive meaning. It breaks down as: **不** (bù, "not"), **为** (wéi, "by" – acting as a passive marker), **人** (rén, "people" or "others"), and **知** (zhī, "to know"). Literally, it reads as "not + by + people + known," constructing the idea of "not known by people." This compact, idiomatic expression is used to describe something that is obscure, unknown, or hidden from public awareness.