Cherchez la femme

Cherchez la femme,  is a French phrase which literally means "look for the woman."
In the sense that a man behaves out of character or in an otherwise inexplicable manner because he is trying to cover up an affair with a woman. Or that a man is trying to impress or gain favor with that woman.

Alexandre Dumas

The expression comes from the 1854 novel The Mohicans of Paris by Alexandre Dumas (père). The first use in the novel reads:
Cherchez la femme, pardieu ! cherchez la femme !
The phrase is repeated several times in the novel. Dumas also used the phrase in his 1864 theatrical adaptation, which reads:
Il y a une femme dans toutes les affaires ; aussitôt qu'on me fait un rapport, je dis : « Cherchez la femme !»
Translated into English this reads:
There is a woman in every case; as soon as they bring me a report, I say, 'Look for the woman!'
The phrase embodies a cliché of detective pulp fiction: no matter what the problem, a woman is often the root cause. The phrase has come to refer to explanations that automatically find the same root cause, no matter the specifics of the problem.

The phrase "cherchez la femme" literally translates to "you search for the woman." The you is plural in this case. That can be determined because the infinitive for "to search" is
"chercher." The "er" has been removed and the ending "ez" has replaced it. This means that the phrase is translated for a plural (or formal) you. If it were for a single (and friendly) you, the word would be "cherches."

The phrase "cherchez la femme," does not mean "search for the woman," though. "Cherchez la femme," is said when the source of erratic or troublesome behavior of a man in sought.

This is not saying that the woman is a cause of the behavior (though one might be). Instead, it is saying that a man has probably acted stupidly or out of his character in order to impress a woman. This may not be the cause, but it is thought to be the source of the odd behavior, so the phrase "chercherz la femme" is used.

The phrase has its origin in French literature. It was originally "cherchons la femme." Because the "er" is removed from "chercher" and replaced with "ons," it means that the phrase "cherchons la femme" means "we search for the woman."

The origin is from 1864 when Alexandre Dumas wrote his novel, The Mochicans of Paris . This is the same Alexandre Dumas that wrote The Three Musketeers and The Count of Monte-Cristo .
The Mohicans of Paris was translated into English in 1878 by John Latey. He had the detective, Monsieur Jackal say, "Where's the woman? Seek her."

The reason this happened in the novel is because a woman was thought to be involved in the crime being investigated. In this novel, a woman was involved.
By 1909, the phrase "cherchez la femme" was known in the United States. O. Henry, whose real name was William Sydney Porter title one of his stories Cherchez La Femme . The line, "Ah! yes, I know most
time when those men lose money you say 'Cherchez la femme' - there is somewhere the woman" is included in the story.