if it ain't broke, don't fix it

/ɪf ɪt ˈeɪnt bɹˈəʊk dˈəʊnt fˈɪks ɪt/

/ɪf ɪt ˈeɪnt bɹˈoʊk dˈoʊnt fˈɪks ɪt/

used to imply that unnecessary changes or improvements can sometimes cause more harm than good