Cicero said, "Assiduus usus uni rei deditus et ingenium et artem saepe vincit."
Translation: Constant practice devoted to one subject often outdoes both intelligence and skill
Commitment is everything. I believe Cicero's words to be the truth but some of us do need to practice more then others to reach the same level.
As for Jelly, I recommend "Deadliest Men: The World's Deadliest Combatants Throughout the Ages" by Paul Kirchner (The illustrator for many of Jeff Cooper's books)
It profiles about 50 or so, including Jelly Bryce, combatants down through the ages devoting a chapter to each, from gunfighters to amazing swords men and women to German dive-bomber pilots. It's a great read if you’re at all interested in the deeds of outstanding individuals.