Something that has no or a very low chance of succeeding or turning out well. The general gave orders to surrender as soon as he saw the battle was a lost cause.Trying to keep a clean house with three young children is a lost cause.
A hopeless undertaking, as in Trying to get him to quit smoking is a lost cause. In the 1860s this expression was widely used to describe the Confederacy. [Mid-1800s] Also see losing battle.