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Of course there are some crucial matches that luck is needed to win especially when both clubs are of the same strength. Dortmund will not reach the semifinals next season because they will face difficult opponents who will be playing them with the mindset of winning them out of the league, and if Dortmund is not lucky enough to play weak club that they can defeat, they might find it difficult to qualify from the round of 16. It is only Real Madrid that have being consistent in the semifinals recently. Inter could not go far last season, even when they played the finals last two seasons. Luck and strength is what a team needs to win UCL.
Yes, you are right. Real Madrid is the most consistent team so far in the Champions League every season. They always qualify for the round of 16 and even higher. This consistency is very comparable to the quality of the existing players and the good performance of the coach, so it seems natural that we often find that they have a big chance of winning the title every season.
Manchester City is the team that has most often threatened Real Madrid in the last few seasons, but thanks to the good cooperation of coaches and players, Real Madrid can be the best to date. Of course we cannot be a guarantee that Real Madrid will remain the same in the long term, that's because other teams will also be very competitive every season to win the title.