I'm not sure if this had been asked before. This is just an example of some odds that I saw recently Fighter A (1.30) vs Fighter B (3.65). With this obviously, Fighter A is the people's champ and Fighter B is the underdog.
Regardless of who is bigger and undefeated record, let's say you have no idea who these fighters are because the names can't even be read like Ulshrkubyki vs Ykwehgyfvbh. If you only have $10 left in your sports betting account, would you go for the champ which you can only earn $3, or go for the underdog which if he got lucky can triple your money?
Never ever try to find connection between odds and people's favorite on unknown matches. As an experiment, I have done the following at past: Bet on two very unknown soccer team that had an odd of x10. Very strangely, two of them greened my ticket but 3rd one failed and the score on 3rd one was 2-1 against my team. If the 3rd one would succeed, I was winning $1000 via $1.
But again, there are moments where teams are unbeatable and undergo doesn't work. For example, some years ago Real Madrid didn't lose a single match in La League, the result was always win or draw and you know, the odds on Real Madrid are almost always low because of how great this team is and how good their performance is.