Let Bygones Be Bygones Meaning

Example : 1886, Thomas Hardy, The Mayor of Casterbridge,  To intrude as little of his personality as possible upon a gay event with which that personality could show nothing in keeping, he decided not to make his appearance till evening—when stiffness would have worn off, and a gentle wish to let bygones be bygones would exercise its say in all hearts.1959, Elizabeth George Speare, The Witch of Blackbird Pond,  You'll find, when you come back, I promise you, Kit, that everyone is willing to let bygones be bygones, and that you can make a fresh start.2003, Ethel Footman Smothers, Down in the Piney Woods,  But I ain't got no quarrel witcha. Just let bygones be bygones.