You can't pick when a loss counts and when it doesn't. Over his career Ali lost fights, should we discount him because of it? Mike Tyson lost fights, does that weaken the claim that in his prime he was one of the best ever? Ultimately, heavyweight boxing is like that. They all lose at some point...except Marciano. Rahman was good enough on the day, and that's it. Had he gone on to create a legacy then we would realise it wasn't a fluke, a one off. But, because he never really fulfilled that potential people are more likely to give Lewis the benefit of the doubt and assume he had an off day. Remember, Lewis two defeats (Rahman and McCall) were against guys he was expected to beat relatively easily. It could be he simply got complacent and overlooked them.