That's football and maybe the team will experience defeat in an unnecessary way and the same as Bayern Munich who lost against Mainz at that time. Regardless of the big win that Bayern Munich got in another match, they must avoid something like that if they want to dominate the Bundesliga again. Leverkusen is increasingly showing the quality of a solid team and Bayern Munich must take them seriously this season because if left alone, it is not impossible that Leverkusen will defend the Bundesliga title for the second season.
Leverkusen doing their best to maintain their position in the Bundesliga such that they are going probably defend the trophy again this season, and if they do, it's going to be the second time in a row and the first time for another team to win the league title twice in a row and the first time Munich is loosing two times in a row, although it's looking like Bayern Munich is trying so hard to make sure to they don't let that record come to reality.
Bayern Munich are currently on top and Leverkusen are following them closely. I think Bayern Munich, who continue to do well with Kompany this season, will not surrender the title easily. Leverkusen's pass based game has made them more and more decipherable. Especially this season Leverkusen seemed to be decoded. Realizing this, Xabi Alonso brought the team back into the race with critical wins in the last few weeks. But Bayern Munich are trying to get back to their old code this season. In my opinion, for the Bundesliga to be an enjoyable league, Bayern Munich's dominance of German football needs to diminish. That's why Leverkusen's wins in the league are of great importance.