What is in our power and what is not

"Off all existing things some are in our power, and others are not in our power. In our power are thought, impulse, will to get and will to avoid, and, in a word, everything which is our own doing. Things not in our power include the body, property, reputation, office, and, in a word, everything which is not our own doing."
The Discourses of Epictetus, tr. by P.E Matheson, [1916], at sacred-texts.com

So training and learning is in our power, but talent resulting from our genes is not. 

You say, "I want to win at Olympia." ...If you do, you will have to obey instructions, eat according to regulations, keep away from desserts, exercise on a fixed schedule at definite hours, in both heat and cold; you must not drink cold water nor can you have a drink of wine whenever you want. You must hand yourself over to your coach exactly as you would to a doctor. Then in the contest itself you must gouge and be gouged, there will be times when you will sprain a wrist, turn your ankle, swallow mouthfuls of sand, and be flogged. And after all that there are times when you lose.
Epictetus, Discourses 15.2-5, trans. W.E. Sweet

Even if we train hard, we might loose. But that is not important. The important thing is that we make progress.

"If you wish to make progress, you must be content in external matters to seem a fool and a simpleton; do not wish men to think you know anything, and if any should think you to be somebody, distrust yourself. For know that it is not easy to keep your will in accord with nature and at the same time keep outward things; if you attend to one you must needs neglect the other."
The Discourses of Epictetus, tr. by P.E Matheson, [1916], at sacred-texts.com

As runner seem to be a fool and a simpleton and we should distrust ourself, if we achieved something extraordinary in the eyes of others. Interesting! All sport mentors are preaching the belief in ourself. Of course we like to think about our strengths, but we should also reflect our weaknesses. Listen to your body. Remember it is the part that is not in our power.

"When you can't control what's happening, challenge yourself to control how you respond to what's happening. That's where your power is."