be a fool's errand

To be a task that has little to no chance of being successful or beneficial. I'm telling you, it's a fool's errand trying to convince the boss to give you more time off. We've been fighting with the city to give us the permit to build on this site for nearly a year now. I'm starting to think that this is a bit of a fool's errand at this point. You're trying to peg him down to a logical, consistent ideology? Yeah, that's a fool's errand.