Gregor has a habit of locking the doors while at home even if it at night. This is a clear picture that he is a paranoid man.
He is also cautious in his activities, therefore may imply that he has a secret that he has hidden from his family as well as other people.
Step-by-step explanation
Gregor undergoes some scariest things that depict unusual situations, but still, he does not stop thinking.
Also, he does not sleep well.
Instead, he gets up earlier and travels to people living in luxurious lives.