If Messi had won all those finals (2014, 2015, 2016), we might not have seen him playing at this age.
For now, this is all speculation, no one can know for sure, but we saw what happened with Yamal, he won the Euros & a domestic treble and started partying like crazy.
I am 100% certain that Flick played a decisive role in calming him down.
Now that he won the World Cup too i am curious to see his attitude in the coming seasons.