Chidi: I'm sorry, Michael, but that's also ethically kind of dicey.
Michael: Here comes the egghead.
Chidi: Well, look, Jason and Tahani are happy together, and telling them that he was once married to Janet might cause them harm. It's not permissible to ruin their happiness to save ourselves.
Eleanor: Wait, but isn't keeping a secret from someone basically like lying though?
Chidi: No, no, it's okay to keep a secret as long as that secret isn't harming anyone, and telling them that secret might cause harm.
Eleanor: Noice!
Michael: Cool. Good point, egghead. I'll tell you what else would cause them harm, getting caught and being sent to the real Bad Place to be tortured for eternity, which will happen if Derek blows our cover.
Chidi: I know, but we'll also be sent to the real Bad Place if we do bad things. I know it's tempting to take a short-cut, but moral strength is defined by how we behave in times of stress.
Michael: Has anyone ever told you what a drag you are?
Chidi: Everyone. Constantly.