Knowing you're here with a purpose certainly makes a lot more sense of life. Provides fuel to keep going, as well.

Like when you see how tough it gets to move ahead and accomplish just one good thing. If you didn't realize what's going on, you might give up pretty fast. But when you think of yourself as an agent with a mission to repair and heal the world, you say, "Hey, there's something major in the way over here! We're taking on a big one now!" After all, the more resistance, the more you must be accomplishing.

That's the idea of the sandpaper. One thing that sandpaper knows for sure--if life is going too easy, it's not accomplishing a thing.