I just built a dining room with iron chairs laid out and a gold table and a sign saying "Everyone Welcome!" at the entrance. And then I realized. Nobody is ever going to see it but me. The only company in the world I live in are the pigs and the other animals/monsters. I'm specifically talking about single-player Alpha, but this can apply to any game mode. It hits hardest when I stay up all night and have a marathon.

EDIT - Oh, and the music. The slow, melodic, melancholy piano that creeps up on you when you least expect it. The soundtrack is "depressing" in musical form.