The spirit of hard struggle can be referred to as the "never-say-die spirit" or the "grit." It comes from the idea of persevering and working hard towards one's goals despite obstacles and difficulties.
Examples:
"Her never-say-die spirit is what helped her overcome all the challenges in her pfe."
Translation: 她艰苦奋斗的精神是她克服生活中所有挑战的动力。
"He has a lot of grit and determination, which is why he always achieves his goals."
Translation: 他有很强的毅力和决心，这就是他总能达成目标的原因。