a tiger can't change its stripes

proverb One will stay true to one's nature, even if one pretends or claims otherwise. After our breakup, he came crawling back, trying to convince me that he'd changed, but I know that a tiger can't change its stripes. You're never going to convince Tom about this—he's too stubborn, and a tiger can't change its stripes. A: "Come on, a tiger can't change its stripes." B: "I thought so too, but the former president really seems to have changed his views on social welfare since leaving office."