Celestia simply tries to enjoy her small moment of peace and quiet. Luna wants to know why they have a game about her time as Nightmare Moon and the War they both fought. Celestia won't enjoy this conversation, that's for sure.
"I ask you, what is the price of a mile? I tell you, it doesn't matter. For we seek redemption, no prize is too small. Only in death, only in sacrifice can we find atonement. This, is our litany."