않은 건

the one who hasn’t

→ 않다
phrase Rare #26,673
the one who hasn’t A contraction of 않은 것은, used to nominalize a negative description or action. Depending on context, it can mean “the fact that … hasn’t” or “the one who isn’t ….”
KO: 아직 준비하지 않은 건 나뿐이야.
EN: I’m the only one who hasn’t prepared yet.

들키지 않은 건 하나 밖에 없거든

You're the only one who hasn't been caught, you know.

— 인생은 아름다워 (1997)