I heard a story once about a man whom God told to push a rock up a hill. It was a huge rock. It was taller than the man's head. But the man said OK - if that's what you want me to do, God, I'll push that rock up that hill. So he tried. And failed. And when the sun set he went away frustrated, telling himself he'd try again in the morning.
For nearly four years the man would wake up early every morning and push against the rock. Every morning, the rock stayed put. He wanted to please God, or at least prove he wasn't completely incompetent, but no matter what he did he could not get the frigging rock up the frigging hill.
Finally, certain that he'd been set an impossible task, he blew up at God: "I've been killing myself every day to move this freaking rock, and it won't move! Why would you give me a task when you knew I would fail?"
But God, in his omnipotent way, said simply, "It was never your job to move the rock. I only told you to push it. I will move the rock." And he did.
The man, exasperated, demanded, "Why bother getting me to push against it all these years?"
So God told him to look at himself. He's grown strong and lean; he now had some sexy muscles; he'd learned persistence, and had become more fit and energetic; he was a great critical thinker, after trying thousands of methods of moving the rock. He'd grown in many aspects, all from those long, hard mornings of pushing against the rock.
It's easy to get frustrated when we feel like we aren't accomplishing things, but maybe the accomplishment isn't the point. The attitude we do things with is more important than the things we actually do. That's the part we have full control over.