Endurance? You've only got to get out there and do it. Face up to it: man was meant to run.
Hard things take time to do. Impossible things take a little longer.
Run hard, be strong, think big!
Vincit qui patitur: he conquers, who endures.
Ignore, then, whether you are tall and thin or short and stocky- whether they laughed at you at home (where they are often unkind) or at school (where they are mostly blind, anyway). Indeed-to hell with the lot of them if you 'feel' you can do it.
The mastery of the true self, and the refusal to permit others to dominate us, is the ultimate in living and self-expression in athletics.