When you immerse yourself in sports science, you learn two things. One, that everything has it's apex: the perfect way to train, the perfect diet, the perfect race strategy, the perfect body composition. And two, you learn how far away you are and may always be from that ideal.
Six hours a day might be the best training volume, but most of us have jobs. A four month training program for your A-priority race may be just the right time to peak, but an unexpected injury might leave you with only 2 months to prep. Most champion runners have bird-thin bones, but most people are born with a thicker frame. Does all of this mean that we can't possibly succeed? If the stars haven't aligned to ensure our success, should we just give up?
No. To say yes would be to misunderstand what endurance sports are all about. Endurance sports are about enduring, overcoming obstacles, weaknesses, and limitations. The fun and the joy and the exhilaration are derived from the challenge, not in spite of it. Those challenges can be external, like a mountain to climb or a distance to cover. But they can just as well be internal, parts of ourselves that hold us back. Mastering one's self may be the greatest challenge of all.
I've always had a low VO2 max. Even at the end of my fourth season of high-school cross country, repeat thousands were excruciating. In those workouts I would get passed by almost every guy on the team, even guys that I would normally beat in a 5k. My lungs just can't process oxygen very quickly. I had mild asthma when I was younger and it probably stems from that. To make up for it I train extra hard on lung-building exercises, and rely on my strengths.
I do have some things going for me, a lot in fact. I'm thin, I have long legs. And even though I've slandered my lungs, they are very efficient. (I recall passing someone at the end of a 10k and realizing that I was breathing half as often as they were. At that point I was grateful that I could go that fast on so little air.)
Imagine if from your birth the doctors knew that you would be the genetically ideal runner. Perfectly proportioned, VO2 max off the chart, the works. As a child your parents gradually let you in on your astounding potential, and told you that with the right training you would be the greatest runner of all time. Your career choice would be a no-brainer, but it wouldn't be terribly exciting or romantic. Your fate would be sealed before you even started. Living out your life would be like reading a book to which you already know the end. When you won your 20th consecutive world title, how satisfying would it really be?
Relish the unknown. Embrace the obstacles. Savor the triumph.