I know that this can sound either incredibly cliché - as we've all heard something like this before - or just plain annoying, but I want to quickly address the seemingly better-than-thou mantra "Once you've ran a marathon, you can do anything."
I started running only because of my high blood pressure, not because I wanted to "conquer" something. Regardless, whether it was trying to run non-stop for one mile (which about killed me at first) or 26.2, something changed - an outlook was renewed. In short, I began to consider running to be a poignant metaphor for life. It's not as though running a given distance affords the runner with a muscular strength to become something in life. But, if the runner correctly focused on his long-distance goal, then his common thought is not so much about finishing quickly, as much as it is about continuing well. It's about perseverance. Fortitude.
The blessing lies in the challenge of not giving up. Now, I say blessing because of what this gift lends itself to throughout our lives. Sure, as a runner, my end goal is to cross the finish line, and as a Christian, to see Christ in the life after, and as Paul said in Romans, await the redemption of my body. But until then, I toil. I muster tools, aids, and tactics that help me persevere well. Nothing in this world "must" be accomplished - save for Christ's work in defeating death and redeeming His Bride. And so, we wait and exist, surrounded by sins that seek to strangle and suffocate us.
I'll put it another way: if I live so absent-mindedly, dwelling only in the what-will-be, I cease to truly, presently be. We are all accountable to exist... and as I mentioned earlier, exist well. That's my take away from the marathon. And sure, you don't have to run to understand this, let alone run a marathon, for we all have races that call us to conditioning. And so, I want to reword that annoying phrase, and reappropriate it for the Christian: "If you're patiently discipling your soul to focus on the step at hand, trusting in the goodness of God in His promises, you are existing well in a righteous fortitude, and in that style, are able to endure."