Both are true, I think - he puts so much pressure on his own shoulders, that it cripples him.
We know that Mitch is very dialed into the narratives around the marketplace, whether that be him being on social media or through his friends/family, etc. He'll have been hearing for several days how everyone has written this core off, and that it's basically over etc., that might have just allowed him to go into last night more relaxed.
I remember going to the Centennial Classic in the kids' rookie seasons at BMO field, and basically all night we were watching Marner - he looked like he was having the time of his life out there. Kid in the playground kind of stuff. We haven't seen too much of fun Marner, especially since the new contract was signed.
The smile needs to get back on this guy's face, because he's an exceptional player that gets in his own way