#4 Mentality
If the last 18 months have reinforced one thing, it is this: Cristiano Ronaldo is stronger mentally than Lionel Messi.
The Portuguese superstar may not be as gifted as the Argentine wizard, but when the crunch moments roll around, Ronaldo bails his team out time and time again. Wolfsburg in last year's Champions League, the final penalty against Atletico, rescuing Portugal against Hungary and eventually winning Euro 2016, scoring the decisive goals against Bayern Munich recently - Ronaldo can be relied upon.
Messi's catastrophes with Argentina have been blamed on his teammates, but a great player does it himself if those around him aren't up to scratch. Even Barcelona's greatest ever comeback, the 6-1 win over PSG, had more to do with Neymar than it had to do with Messi. The Argentine spurned a ton of chances against Juventus as well, with his team crying out for inspiration.
In this El Clasico, Barca will be looking for leadership from Messi, but if recent history is anything to go by, they're better off looking elsewhere.