不屈不挠--------keep one's chin up

例句：
A: I'm deeply impressed by his diligence and perseverance.
我对他的勤奋和毅力印象深刻。
B: Me too. Although he has failed several times, he still keeps his chin up.
我也是。虽然他失败了几次，但是他依然不屈不挠。

同义词：
as steady as a rock
firm and unyielding
fight for tooth and nail
hang on by the eyelashes
stick to one's color