Thin line?

Tears and Laughters (PC: Myself)

  "This is my last message to you: in sorrow seek happiness."

                                                        - Fyodor Dostoevsky 

                                                            ("Brother's Karamazov")

The devil and the angel were in moods at extreme ends of the spectrum. One was overwhelmed with joy, while the other seemed deep in sorrow.
"You look sad, What happened?"
"I am not very sure. But maybe it is because I got all that I wished for."
"Oh, but that is precisely the reason I am so happy. I too got all that I wished for."
"Happy for you!"
"But how does it make you sad?"
"The way it makes you happy."
"Is it a very thin line?"
"Maybe. I don't know."