it's upsetting when the underdog win which you hopefully will not because most of the time the analysis is that a champion will always be the favorite and the odds speaks for it. if you are going to be banking on the underdog, it could just mean that you are really a fan of that MMA fighter which could be entertainment for you. but for a broke man who wants to win big but has small capital, he meant money and might just bet his $50 to win 3x rooting for the underdog.
Many bettors place their bets on underdogs not because they are fans of them, but because they see (or think they see) underestimation of the underdog. For example, if you see that the bookmaker gives a odds of getting a 6 when throwing the dice as 1:5, then most likely you will not bet, right? But if you see the odds for the same event 7 or higher, then you will make as many bets as you can, because it is profitable and not because you are a fan of 6s.