Money was the reason why I passed on two opportunties as I posted recently A) as a 'potential' pro footballer and B) a nailed on job as a football journalist. There was a third actually because when I boxed as an amateur my trainers said I had the ability to turn pro. Now there's always been plenty of money in boxing, so that wasn't the reason I refused. Cutting straight to the point, I didn't agree with my trainers. I did very well as an amateur but there's a world of difference between that and the pro game. It's a punishing life (training, sparring, roadwork, dieting, making the weight etc) even when you aren't getting punched - and pros know how to do that. Properly. Even as an amateur I could hardly believe how brutal, and I mean brutal, the training was and that was just gym work, weights, sparring with other amateurs and circuit training.
Okay, my trainers were utterly fanatical about fitness but they reasoned that it was essential to give you that edge in fights. Football training at my level was a doddle in comparison. So I gave boxing a miss mainly because I didn't think I'd be good enough as a pro and end up being a journeyman punchbag for up and coming talent.
Mind you, given the chance to be a world class footballer or a world champion boxer, I'd choose being a boxer every time.