믿는 도끼에 발등 찍힌다. (be betrayed by someone you trust, be backstabbed)
믿다 (v.) to believe or trust
도끼 (n.) ax, A hand tool used to cleave a thick tree or chop a firewood.
발등 (n.) the top of the foot
찍히다 (v.) To be struck with a bladed tool, etc., or stabbed with a sharp thing.
Semi-polite/polite – 믿는 도끼에 발등 찍힙니다
>> This expression is a metaphorical way of saying that something you thought was going to go well turns out differently than you expected, or that someone you trusted betrays you.
>> Originally, the phrase was used to describe a situation in which a person trusts a good ax to chop or split wood, but the blade slips from the handle and has harmed the user.
>> So, it’s become an idiom to say one shouldn't put too much faith in someone who is close, because it could hurt you or get you into trouble.