I’m going to agree that this game is his career, but disagree with you about what it means.
First of all, being a backup NFL QB is a different trade than being a starting NFL QB.
A starting NFL QB is the center of attention all the time. He gets starter reps, a game plan designed with him in mind, all week being prepared to be the key player in the upcoming game.
The backup QB has the job of being ready to step in if disaster occurs and the starting QB goes down, and then to make the best of a bad situation. He’s like a fireman answering the bell, he knows he’s going to have a mess to deal with. And he doesn’t know what he’ll be walking into, just that it will be bad.
The career backup QB has to have a different mindset. You’re right, this game is his career. Stidham is a career backup QB.
So his focus for this game won’t be the opportunity to become a starter if he does well. His focus will be on not letting his teammates down, not making the mess worse by crapping his pants, making the best of the situation. And with that focus, and the mindset of a backup QB, a lot of the psychological factors and pressure outsiders expect to affect him just aren’t in his reality.
He should play like a backup, doing his job. That’s what he is. If he tries to play like something he isn’t, like anything other than what he is, he’ll do poorly. If he just does his job he may not win the game but he’ll do better than most people expect.