We see so many who start with an innate advantage -- even at the start of their career, it is clear they are special. Fighting sense, an undentable chin or an athletic advantage. Who started out bad but improved gradually through hard work?
Rocky Marciano, maybe? Couldn't make it in baseball, turned to boxing. Undersized as well as left so much to be desired on defense, yet, made up for it all with hard work -- and a God-given Suzie-Q of a right hand.
Marciano is the first name that comes to mind. His work ethic and determination were uncommon. Marvin Hagler is another. He had talent for sure but wasnt the most talented he developed his skillset through hard work and dedication.
Many ATGs' greatness are largely due to their very hard training and discipline, starting to learn how to box and train seriously at a very young age, having a long amateur career, etc. If Frazier didn't train so hard, he might've gassed out and been knocked out by Ali once or twice, and Hagler might've broken down first against Hearns if he wasn't trained like a ****ing machine. Oscar might've achieved much less if he started to box at Sergio Martinez's age. Same could be said for Floyd or JCCSR. Most of these guys had great talent, but talent without hard work only takes you so far. EDIT: Except TKO6.
Jersey Joe Walcott is my number one for grit and hard work. Also in a different way, Nigel Benn, he definitely gave himself a longer career after reinventing himself post Eubank I, he worked on both stamina and boxing skills. The Benn of Eubank I or Michael Watson would have been KO's in one by McClellan.
Juan Diaz, man. This is a kid who came out of nowhere. Nobody in the know thought much of him. He went pro too early, he didn't have any strength, he slapped, and he was hittable. I had heard that he was an animal in the gym, but didn't think anything of it. Kid exploded in like two years. Watched him against Lavka Sim and couldn't believe what I was seeing.
I'll add a surpise one here: Jack Johnson. He took on Choynski, fully knowing he'd be KO'd, just to be able to pick up knowledge from him. Now that's learning the hard way. Armstrong should also be mentioned.
