I think that stamina is predicated on intense training BUT genetics can play a part in enhancing OR depleting one's stamina. Example - a person that is genetically programmed to be "nervous" can train hard and build up his/her stamina, but in a stressful (boxing) situation, their stamina will be depleted because of the expenditure of nervous energy. Grebfan9 www.firstroundboxing.com
You have to word like Hell for good stamina. Some of it is genetic, but it's almost all extremely hard work.
Pacquiao best stamina in boxing honourable mentions Calzaghe and Diaz Hopkins has great stamina but also relies on pacing himself Floyd too.
Very good point that I hadn't thought of. Being out of one's comfort zone, on stage, and bright lights would have a bigger affect on one's stamina than somone publicly outgoing like Ali. Shy boxers might want force themselves into public situations a lot preceeding a fight.