하나를 보면 열을 안다
hanareul bomyeon yeoreul anda · See one thing and you know ten.
One small action shows you what someone is like overall.
When to useJudging someone by how they treat waiters, or how they keep a small promise.
Examples
첫 만남에 직원한테 반말하더라. 하나를 보면 열을 알지.
He was rude to the waiter on our first date. See one, know ten.