be undaunted by repeated setbacks 百折不挠

“百折不挠”，汉语成语，意思是无论受到多少挫折都不退缩（never yield in spite of reverses），比喻意志坚强，品节刚毅。可以翻译为“be undaunted by repeated setbacks；dauntless；relentless”。

例句：

百折不挠的精神

unyielding/relentless spirit

尽管他的想法屡遭非难，他似乎仍然百折不挠。

He seemed undaunted by all the opposition to his idea.