The Irish Times posted a great article about why Africans dominate distance running. It's centered around an interview of Paul Tergat, one of the greatest runners of all time. There are a number of interesting quotes from it, but the one I think I'll call out isn't so much about why Africans are better, but about how Tergat got into running:
“After school I joined the military, and one coach said ‘hey, young man, in the running, you are good’. He changed my life. No one in my life ever told me I was good. Growing up we struggled just to get something to eat.
“So when somebody tells you that you are good, that you have potential, it will change your life. It gave me the motivation, to believe more in myself. And I started to push myself.”
I encourage you to do two things. First, read the article. It's worth it. Second, if you know someone who has the potential to do well in anything--it doesn't have to be running--make sure they know it. Just tell them. Sometimes that's all it takes to get them on the path to greatness.