It's 'useless' trying to change her mind. = It's 'useless' to try to change her mind.
Drugs are 'useless' in treating the condition.
I made a 'useless' attempt at fixing the leak.
(..) - Of cause you'll take it. Cause you have no teeth, you have no balls, kid. Look, I am stuck here. Why don't you find something useful for me to do. Unlike you, I am not useless. And I maintain my own property. These swamp rats, on the other hand, you just can help it. How long do I have you for? (..)2008 Gran Torino