If you go through the fixtures of the uefa champions league round of 16 you will see that most matches there are not tough, we already know the clubs that will be knocked out in the round of 16. It will be hard for an upset to happen because those big clubs will want to score so many goals against the weak clubs to make the second tie easier.
The easy running clubs are craving for important phases and good rewards. The mediocre teams are not competitive hard enough, but they have this thing called "lucky stars" which serves an important aides for these clubs. The fixtures we have are not competitive enough, there are matches that are consider tough but we have to keep our ears to the winning sounds. Normally, we don't have tough matches in the UEFA Champions League round of 16. It will be simple to decide which team will ascend to next phase of the UEFA Champions League competition.