This story appears in ESPN The Magazine's August 21 Fighting Issue. Subscribe today!
When boxers prepare for a fight, it's a process of daily accretion. They sharpen, strategize, suffer, reveal their own weaknesses, then correct them. And few see the process more than a sparring partner. So what makes Floyd Mayweather so great -- and the overwhelming favorite to beat southpaw Conor McGregor on Aug. 26? For the answer, we sought out boxers who have worked with Mayweather in recent camps where he's been preparing to fight left-handers. Two of them, Zab Judah and DeMarcus Corley, lost unanimous decisions to Mayweather.