Did Wladimir Klitschko's KO losses to Ross Purtity or Lamon Brewster ruin his career? Did Manny Pacquiao's KO losses to Torrecampo and Singsurat ruin his?
in Manny's case no, but you must admit Klitschko became a safety first jab master in the wake of his loss to Brewster...i remember that fight, when K was ahead and fighting agressively the commentators raved about his "American style"...well that was gone forevever after that loss. klitschko morphed into The Most boring, over caitious, overprotective HW in history and quite possibly the most boring and overcautious fighrer in ANY division in tbe history of the world.
It really depends on the fighter. The eras were so different because back then, during the depression, fighters were fighting to put food on the table, so a loss was taken with a grain of salt and they were back in the ring a few weeks later. Today a loss is devastating to a fighter with a win streak who suddenly discovers he's human afterall. Sometimes they come back, sometimes they find another occupation, but most of the time you will see a very long layoff - much longer than they are used to - before lacing them up again after the bruised ego has time to heal.
Joe Louis deserves a tremendous amount of credit for suffering such a beating, and then going on to set the current world record for longest reign and most defenses. I think the loss actually helped him become more self disciplined.
I have seen good fighters ruined by lesser beatings. He did well to come back from it the way he did.