In sports, there is always someone winning dominantly. It can get to a point where they are almost always expected to win. By that point do you continue to bet on those favorites to keep winning or does it bore you? Would you enjoy stirring it up a bit just for the fun of it and betting on the underdogs even if the chances are quite low?
I did this with Liverpool last season I lost miserably. Before playing a big team that have been winning consistently, I have learnt to weigh the how much they value that match and if they will be able to play with all their power and might. When it is obvious that they can lose the match and it will not make any difference to them, they wouldn't mind losing the match especially when the opponent need to win the match and will give their best. This is why I do proper evaluation of every match I play so I don't go putting my money in a match that has low probability of success.