be fighting a losing battle

To be trying persistently and with great effort to do or achieve something that is ultimately doomed to fail. You're fighting a losing battle if you think you can convince Sarah to go to college. It looks like I'm fighting a losing battle trying to get a raise from my boss. I'd give up trying to get your brother to agree to this deal if I were you, You're fighting a losing battle, man.

be fighting a losing battle

COMMON If you are fighting a losing battle, you are trying to achieve something, but you are very unlikely to succeed. Recent research by doctors in Los Angeles suggests that very overweight dieters may be fighting a losing battle. Theatres compete with the movies and DVDs and they're fighting a losing battle.