선무당이 사람 잡는다

Etymology
First appears in the chengyu-ized form 生巫殺人 in the 公私恒用錄/공사항용록 Gongsa hangyongnok, c. 1800, as an example of a native Korean proverb.

Proverb

 * 1) "the novice shaman kills the person [that they were trying to heal]"; a little knowledge is a dangerous thing