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This happened because they were too quick to sell players just because they wanted the benefits they had which resulted in De Zerbi inevitably becoming a victim to be fired by Brighton before.
Brighton had always been one of the clubs that produced stars and they became one of the dark horse clubs that were very wary in the De Zerbi era but mistakes in transfers that released too many star players such as Trosard, Caicedo, MacAllister, Bisouma, Cucurella or even Ben White actually became the beginning of destruction where they increasingly lost momentum because their core players left and there was no good backup as a replacement.
Now they are back to trying from scratch but of course it takes time so for this season I don't think we can expect much more from Brighton as it would be great for them to be in the top 10 as well.
that's true, and that's the main reason why De Zerbi resigned from Brighton, he avoided dismissal. The transfer policy taken by the management is likely to be the trigger for the manager to decide to resign, it is clearly not in line with his plan to build the team. However, most mid-table teams maintain their existence with a business model of buying and selling talented players in every transfer window.
Brighton performance so far is still quite good, even better than Manchester United who they defeated in the second week of this season. Brighton has the opportunity to finish in the European zone if they are able to create many surprises when facing elite teams, and get full points when facing other mediocre clubs. De Zerbi is now performing impressively with Marseille in Ligue 1.