Mood ...

Look around. On any day there is reason enough for any person to be in any mood—happy or unhappy, hopeful or hopeless, heartwell or heartsick—so that 'Why are you in such-and-such mood?' may reasonably be answered: 'X and Y and Z.' But, at least in my experience, moodish reasons are generally not moodish causes. For me, there's almost always a causal inexplicability to moods, an arbitrariness. They seem to come in from and go out to: nowhere. First I am sad, sighing over everything. Next I'm happy, smiling on the world beatifically. Then I am depressed, wanting to pull completely away from everybody and withdraw sullenly into myself. Meantime the external conditions of my life are unchanged. So what gives?

'Mood is like the Niger River in Africa; no one knows its source, no one knows its outlet—only its reach is known!'

—Johannes Climacus, K. XII.1.237.

(Note: To the detriment of the analogy, the source of the river was discovered in 1879. How rude!)