#1 The away goal
1-1 isn't the worst result if you think about it. What it does do, though, is hand Atletico Madrid an immense advantage in the form of the away goal. In a week's time, at the Wanda Metropolitano, Arsenal will either look for a 1-0 victory to proceed to the finals of the UEFA Europa League or will have to score one more than every goal Atletico manages to net.
The problem with that is Atletico Madrid's intimidating home form. The men in red and white haven't lost a single La Liga game at home this season, winning 12 and drawing 5. Further, they have scored 28 goals in these 17 games and have only conceded 4.
To add to that, Diego Simeone's men haven't conceded a goal in 11 home games - that's a jaw-dropping total of approximately 16 and a half hours.
With facts like these facing them, Arsenal will definitely have to play out of their skins and will have to come up with something special to beat Atletico Madrid and progress to the finals of the Europa League.
The away goal rule is bound to come in to play and could cause Arsene Wenger and his side some headaches.
You just can't help but wonder though - Last night's game seemed to be Arsenal's. What if they had buried it so it didn't come to this? What if...