if that said person got schooled and KO'd by a complete bum then yeah, I might lose a little bit of respect.
But if the person is getting older, or just got caught by a lucky shot, or simply lost to someone who was better, well that's the way the sport(s) go. Can't win them all.
There is a very small percentage of fighters that go their entire careers without getting knocked out. Especially in boxing. It usually happens eventually even to the best (like Ali, Sugar ray robinson, Leonard, etc.).
Takes a very special and unique type of human (and very thick skull) to never get KO'd. Guys like marvin halger, bernard hopkins, etc., just something about their skulls and ability to absorb shots that is just not normal.