You can be favored to win every game on your schedule, but that does not mean you are expected to go undefeated.  Along with the probability of winning a given game, is the probability of losing that game.  If the probability of winning is 75%, it means the probability of losing is 25%.  And when you consider the probability of losing any given game, over the season (or over the last 3 games) it means there is a very high probability that you will lose at least 1 of the games.