Sometimes, I'll go on long mental journeys. I'll be thinking about one thing, I'll find some logical conclusion of that one thing, and then I'll exclaim to myself: well, if that one thing is true, then certainly this other thing must also be true!
And then I'll start thinking about that other thing, which will lead me to that other thing.
And eventually, I'll fall asleep. That's my idea of an evening well spent.