Ok, maybe (I really wouldn't know, but why not) we should start by solving the BP chicken-and-egg problem. The solution for the actual chicken-and-egg problem is of course simple: the egg came first. Really.

But which came/comes first: mania or depression? There's depression after mania, but there's also an egg after a chicken.

Another question: should stability be our aim or functioning despite instability (or both)? That's rather important in solving a/the puzzle, I think.