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Chelsea can certainly lament the fact that despite spending so much effort and so much money, they are not seeing any improvement in their squad. Only to improve the team, the team is spending significant amount of money to buy players as well as appoint experienced manager to Chelsea but still the position of the team is not changing. A new manager taking charge of the team every season could be one of the reasons why this team has not improved in performance. Every season when a new manager takes charge of the team, every new manager wants to implement his own strategy which may affect the performance of the players by adopting a different strategy every season. A quality manager must be appointed and this team will do well in the long run.
Pochettino is an experienced coach in the Premier League, but Chelsea cannot fully expect him to change everything in the first 5 matches of the season. So far Pochettino is still considered a failure because he has not proven a significant improvement in the team's performance, but if Chelsea can give him more time then I think Pochettino is ready to make a lot of changes.
Chelsea's performance is unstable because they are still unable to establish good cooperation between their players. The team's performance is affected by the number of new players and new strategies, so it's natural that this team hasn't been able to play well in many matches. I don't completely think Pochettino has failed this season, but he has only failed in his last 5 matches in the Premier League.