"Lost one's marbles" is an idiomatic expression that means someone has become mentally unstable or crazy. There are several synonyms for this phrase, including "gone off the rails," "dropped the ball," "lost the plot," "flipped one's lid," "lost one's mind," or "gone bonkers." These phrases are used to describe someone who has experienced a mental breakdown or is acting irrationally. "Lost one's marbles" and its synonyms are often used colloquially to describe situations or people who have become difficult to deal with or are acting in an unpredictable manner. They suggest a sudden loss of control or a break with reality that can be alarming or confusing for those around the person experiencing it.
