In short, you can say that Chelsea was a more experienced team as compared to PSG, and this thing came to their advantage. PSG weren't comfortable and were feeling the pressure of the final. That is the reason that Chelsea took early advantage in this game and quickly scored three goals in the first half of the match, making the match totally under their control. Palmer scored two back to back goals and gave early advantage to his team.
PSG had such a big semi final game where they beat the giant Real Madrid by 4-0, but in this final they completely collapsed.
Chelsea's biggest plan was to attack PSG's confidence and they succeeded in that plan. Chelsea's plan personally seemed great to me. They started playing aggressively on PSG from the start and completely destroyed PSG's confidence. Although Chelsea's plan was very risky, they used their experience and courage to win the match against PSG by a large margin.
A team brought down the flying PSG from the list of weak teams of the tournament. Seeing the performance of the last season and the beginning of the tournament, no one might have dreamed of Chelsea. Because Chelsea's performance was very bad and they seemed weak. Even PSG was unstoppable from the last Champions League knockout match. With such statistics, Chelsea won the match and made the FIFA Club World Cup known as a field of unexpected results.