In vain
If you do something in vain, it means you try hard to achieve something but fail. Your efforts do not bring any success or results.

Examples:
1- The doctor did everything possible, but all their efforts were in vain, and the patient did not survive.
2- On January 26, 2020, Kobe Bryant, a popular American basketball player, and eight others died in a helicopter crash. Despite emergency responders' efforts, their attempts to save them were in vain, leading to worldwide mourning.