I don't understand the grand scheme of things.
Neither does any of us, which is some comfort.
The greater design, the complexity of Providence, is far beyond any human being's vision. And that's a good thing. I don't want to know the future or be able to comprehend exactly where we're all headed, as a society, as a world. My head is filled already with the limited number of things I'm supposed to understand, so I'll gladly leave the rest of it to God.
My piece of the design is very small, barely even a blip in the history of the human race.
It's tiny, but it's there, just like your tiny blip and the tiny blip of every other human soul.
So, if I feel silly or ashamed or disappointed because something goes wrong, or just doesn't go the way I expected, I try to pull back, contemplate the great design, and acknowledge my smallness. I also acknowledge the fact that I don't know my purpose here. I can take my best guess, and try to serve in the way that seems appropriate, but the deeds that appear most important to me may actually be completely insignificant.
Writers may be tempted to assume their writing is the most important service they will ever perform for others.
It may be. It may not be. We can all see, now, that the writing of C.S. Lewis was his life's purpose, his contribution to the great plan. But a C.S. Lewis is rare, and most of us writers know very well that we're not on that level!
It may be that my purpose is raising my daughter to fulfill her own purpose. Or, I may unwittingly accomplish my life's chief mission in some random five-minute encounter with a stranger that will slip out of my memory in a day or two.
I hope that in heaven, we'll get to see movies (or dreams, or something along those lines) about all the purposes that were fulfilled that we never understood while we were here. I look forward to that enlarged vision in which I will see all the beauty and staggering intricacy of the great design.