What does the expression “to wash one’s dirty laundry in public” mean and Where does it originate?

All we did, about a century ago, was to reverse the French proverb, it faut laver son linge sale en famille, “one should wash one’s dirty laundry in private.”

The French idea, that is, is that family quarrels or matters that concern members of the family should be kept within the four walls of the home.

Anthony Trollope seems to have heard the French saying, or was at least the first to give us the English equivalent.

This was in The Last Chronicle of Barset (1867): “I do not like to trouble you with my private affairs;, there is nothing, I think, so bad as washing one’s dirty linen in public.”