[michael9423]

How can he be sure he's a theoretical physicist if he doesn't know reality exists at all?

The truth is, instead of reality, he would be better off questioning theoretical physics, which indeed does not exist outside the heads of academia.

His "questioning of reality" only happens philosophically (in other words, it is an academic farce), once he gets up to do some grocery shopping he sure knows what to buy so he can eat in order to survive. There is your objective reality.

Humans understand reality if they do not bury their heads in the sand. But academia can get in the way.