...if you just trained everyone, that they would all be able to:
break 20 minutes for 5k
run a 5:30 mile
or whatever
The reason is simple...runners like to believe that they achieved whatever success they have MOSTLY because of the hard work they put in. They don't like to believe that they were given a head start with genetics.
It's ok to accept that (if you are even remotely good) that you were blessed with the genes.
Successful runners work hard. There is no denying that. There is also no denying the fact that hard work and consistent hard work for years pays dividends. But, what is even more true is that we are limited by our genetics. We just are. Just as most of us here will NEVER be able to break even 14 minutes for 5,000 meters no matter what we do to try, MOST of the general population could not and will not break 20 minutes for the same distance...they just don't have the physical tools to do so.
You can train some farm horse as much as you want...doesn't mean he'll be able to compete in the Kentucky Derby.