#4 Mauricio Pochettino still has much to learn
Having been forced to change the personnel for his system, Mauricio Pochettino could be forgiven for going with a circumspect midfield of both Moussa Dembele and Moussa Sissoko. However, with Arsenal nervous going into the game, playing Heung-Min Son would have placed the Gunners under early pressure, as the Korean showed in the game against Liverpool.
Instead, Arsenal were allowed to dominate the middle of the park, with the Gunners having the impetus. Pochettino's struggle to change things around when things do not go right from the start ensures that his record against big teams will continue to be bad.
Fernando Llorente and Son actually caused Arsenal some trouble in the final few minutes, and perhaps if they were brought on earlier, things could have been made different.