Tools of the Trade
Desire. For some jobs, you don't have to be especially hungry for clout and shiny trophies to be good at them. Boxing is not one of those jobs.
Health, healthcare, and then some. Not only do you have to be ridiculously athletic, and basically a semi-professional-grade runner, but you may have to drop ten pounds at the drop of a hat. That takes a serious knowledge of your body and power over it.
Discipline. Even if you only fight once every month or two, this job consumes your life. It eats it up. You've got to be able to keep things in perspective.
Support. To take on a career as challenging and potentially draining as this one, you've got to have your family, friends, and fans behind you 100%.