Errors in the first concoction, are hardly mended in the second. [ Proverb ]

Old houses mended cost little less than new before they're ended. [ Gibber ]

If I might venture to appeal to what is so much out of fashion at Paris, I mean to experience, I should tell you that in my course I have known and, according to my measure, have cooperated with great men; and I have never yet seen any plan which has not been mended by the observations of those who were much inferior in understanding to the person who took the lead in the business. [ Burke ]