In the 1st season of True Detective one of the very few things in Rust's apartment back in 1995 is a very small mirror, just large enough to reflect a single eye, which he repeatedly looks into during the whole season. And he doesn't seem to have any other mirror at all.
In fact in S01E04 Marty (more or less jokingly) asks something along the lines of
You supposed to see both eyes in this one?
But what is the purpose of this mirror, what is Rust expecting to see in it and what does that in turn tell us about Rust? I see that he has quite some many strange quirks about his character but they also don't just come out of nothing. So how does Rust's weird one-eye mirror tie into his character and his attitude?