鼠

it doesn't matter whether a cat is white or black; as long as it catches mice it's a good cat (variant of a Sichuanese saying used in a speech by Deng Xiaoping 鄧小平|邓小平[Deng4 Xiao3 ping2] in 1962, usually associated with his economic reforms starting in 1978, in which pragmatism was favored over ideological purity)

lit. one pellet of rat feces spoiled the whole pot of soup (idiom) / fig. one bad apple can spoil the whole bunch

see 一粒老鼠屎壞了一鍋粥|一粒老鼠屎坏了一锅粥[yi1 li4 lao3 shu3 shi3 huai4 le5 yi1 guo1 zhou1]