Chelsea's mistake in recruiting young players who don't have enough experience seems to really affect the performance of the Chelsea club and I think Chelsea chose young players because they thought the young players still had strong energy but in fact it actually made their performance worse and the young players couldn't perform. solid with other teammates, so it is difficult for Chelsea to build up the club's performance, in fact Chelsea is increasingly experiencing a decline.
Mauricio Pochettino as coach has not been able to do his best to improve the team's performance and it seems that Mauricio Pochettino is having difficulty managing his subordinates so they can recover from the downturn experienced by Chelsea.
Usually recruiting young players is because it's believed they have the strength and capacity to run and play a complete game without getting tired most times, and they usually are less prone to injuries as they are still very strong, they also have good sprint advantage aswell as they usually have a decline in sprint as they age, as seen with most old players.
Experience is aswell very important as it will be needed for decision making and other need actions on the pitch but sadly it's most Common with young players as they mostly lack experience with league games as it's usually their first time playing for the league and probably working with their coaches and I think this is the case of Chelsea as the boys are mostly young and new to the team.
It will take them really sometime to get used to the coaches tactics and with the new leagues they are been introduced to as some of them may not have played in the premier league before, the old player who have been in the team before the arrival of the new ones will aswell have some challenges getting along with the new players and their play styles.