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As I already said, the next season will be decisive - if Arsenal does not take the title, then progress will be replaced by regression.
Arsenal must be able to win the title next season. They already have a solid squad and they have been runners-up twice in the EPL. I'm not saying Arsenal should be EPL champions because that's quite difficult. But at least Arsenal can get one trophy this season. The Arsenal squad is currently in their best performance. I think if they fail to get the trophy again this will affect the players' confidence.
Arsenal must at least deliver the same performance like last season. Arsenal performing quite well last season, but due to the small mistakes, and it cost them trophy. I was very disappointed how Arsenal lost the important games twice in a row last seasons. But, it must be a very important lesson for them.
I must admit, Arteta has been transforming this club well. But, as you can see, their mentality was the main issue.
Arsenal have failed to get the trophy two times. It was because Manchester City backstabbed Arsenal at the end of the season. I think player confidence will stay the same. But, failing three times in a row will frustrate them. It's possible for Kroenke, Arsenal's owner, to sack Arteta from the club.
The previous season, Arsenal managed to advance to the quarter-finals before finally being defeated by Munich. I think it's already a good result but they deserve to go further in the UCL.
The failed in the UCL last season, and it's proven they were not deserving to go further in UCL. But Arsenal almost beat Munich. I would not say Arsenal played badly in that game. They must be coming back stronger than last season. Last season, they failed against Bayern Munich, but i hope they will able to beat any big teams in UCL.
All in all, strengthening their mentality is the biggest improvement to be done by arsenal.