What it means
To lose your marbles means to go a bit mad, act irrational, or make decisions so daft people start looking at you sideways. It’s usually said in a teasing or half-concerned way, not as a serious mental health label. If you’ve lost your marbles, your common sense has basically rolled under the sofa and refused to come back out.
Usage examples
"He blew his last fifty quid on a novelty sword and reckons he’s starting a dojo in the lounge. Dad: you’ve lost your marbles."
"Have you lost your marbles, you cannot drive to Scotland and back in one day just for a sandwich."
"Gran reckons the council have lost their marbles building a roundabout where the duck pond used to be."
"You've booked a 6 a.m. flight for a night out in Ibiza and you haven't even packed. You've lost your marbles."
"Mum said I've lost my marbles for paying twelve quid for a sandwich at the station, and fair enough really."
Where it comes from
This phrase is old-school English and goes back to marbles meaning a person’s wits or mental stability by the late 19th century. The picture is dead vivid: if your marbles scatter, your mind’s not all together anymore. That playful image helped the phrase stick in both British and American English.
Other ways to say it
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