좋은 건

the good one; what's good

→ 좋다

phrase Uncommon #11,668

the good one; what's good 건 is a contracted form of 것은, combining the noun-modifying form 좋은 with a topic marker. Depending on context, it can mean “the one that is good,” “what is good,” or “the fact that something is good.”

KO: 좋은 건 오래 간다.

EN: Good things last a long time.

좋은 건 믿지 않지

I don't believe in good things.

— 잠입자 (1979)

기분이 안 좋은 건 알아요

I know you're in a bad mood.

— 타이타닉 (1997)