Why did an angry Lionel Messi call his Barcelona teammates childish after loss to Atletico Madrid?

An enraged and frustrated Lionel Messi has accused his teammates of making “childish mistakes” after their 3-2 Supercopa defeat at the hands of Atletico Madrid on Thursday.

The Catalan giants fell behind to a Koke strike a minute after half-time, but goals from Messi and Antoine Griezmann in minutes 51 and 62, respectively, saw Ernesto Valverde's side lead 2-1.
They held the advantage until the final 10 minutes, but mistakes in defence saw Alvaro Morata score an 81stminute penalty, before Angel Correa completed the comeback five minutes later.
This annoyed Messi, who didn’t hide his irritation after the game.
"It is a shame, we played a great game, after so long we felt good again, we were in control, dominated and attacked all the time," Messi told reporters.
"We let it slip through certain mistakes when [Atletico] were already almost dead, in less than 10 minutes they turned round a game that we should have seen out.
"It hurts because it is a title and we wanted to be in the final and win it, we showed a different side to what we have been showing recently against Espanyol and at the end of last year, we played a good game but sadly we couldn't get the victory.
"We have taken a step forward today [Thursday] despite the defeat but we are aware that we have not been doing things the way we want, we do not want to make these childish mistakes again."
Messi and his teammates don’t return to action until Sunday, January 19 when they host Granada at Camp Nou.