I refuse to admit defeat. 我绝不认输。
It's not over until the fat lady sings. 鹿死谁手,犹未可知。 I never concede a point. 我从来不肯做半点退让。
Stand your ground. 要坚定你的立场。(要站稳你的脚跟) He won't cave in to public protest. 他不会向群众的抗议屈服。