Read this:
Sub Elite Runners Chase Improvement
And then read this:
In many ways marathoning is the modern version of Sisyphus and the stone. We try and try and train and train, and we hope that one day that stone stays at the top of the hill, but deep down, we know it won’t…perhaps we wish it won’t. For the journey is what makes me tick. The never ending quest for improvement, for a little more speed, a touch more stamina, a bigger smile at the finish line no matter how hard the race. There are days where I wish I didn’t have the stone, where I wish I could be lazy. But I need that stone. I love the stone. And I plan to push it up the hill for the rest of my life. For what is Sisyphus without his stone? Just an ordinary man, not myth or legend, or figure to cheer or pity. With his stone, his burden, his mission, he is the stuff of legend.
This Running Life 
I like this a lot. When I was training for my first marathon, the Miley Cyrus song “The Climb” was popular and my wife and kids played it when I would come back from a long run. It was great motivation for what seemed an almost impossible task at the time. She bought me a RoadID bracelet with the title, “It’s The Climb”. I still treasure that memory. I Am Sisyphus brought that all back. Thank you.