Consider that the favorite of something often has favoritism or some definite advantage going for them to make them the favorite e.g. more skill, more money, better odds in their favor for some reason, etc, and the underdog does not and must make the best of things - possibly winning by hard work, quick thinking, and/or simply luck. Here’s a theory I sometimes discuss. I think many people can remember when they were kids and not picked to be on some team - perhaps having been smaller, weaker, less talented or simply not liked as a person. Later in life they may apply that remembered sense of unfairness towards influencing their picks in sports or some other endeavor. For example, the best team in sports often has more money, more talented recruiting, etc to get the bigger, faster, more skilled players. Identifying with such a situation then may lead some people into picking the underdog. Whether or not the underdog actually wins, it may make them feel better about an imagined sense of justice or that hard work can sometimes overcome the odds. Of course this sometimes can be a disaster when it comes to gambling. The concept of the underdog is often used politically and may use my argument as discussed here in a way to try to try to persuade people’s viewpoints about justice, right and wrong, etc, for example, calling one country an underdog versus another to push vested interests.