Even quality players will inevitably make silly mistakes, they're just human after all.
I watched Inter v Barca yesterday, and at one point after a corner kick, the ball fell to Lenglet in a clear cut chance to score. He missed the sitter terribly and fell to his knees, holding his face in shame. Immediately after, I think it was Umtiti or someone else who came up to him, lifted him from the ground and told him something like "don't worry about it, it happens, don't get stuck on this and play on". This is the true way to deal with teammates' mistakes, not throw childish tantrums because things don't always go as you expect them.
Someone should remind Auba of all the sitters he missed last season, some of them truly shocking. And I absolutely love Auba, have loved him even before he joined Arsenal. He's not fit to be captain though.