The final moments of the show are a careful implementation of this advice. The very last two sentences of the finale, if interpreted according to the ordinary cultural connotations for "light" and "darkness," provide a note of hope at the end of a grisly but heroic adventure. The darkness seems to occupy a lot of territory, yes, but once the whole universe was all darkness and no light - and now the light seems to be winning!
However, relating his near-death experience just seconds earlier, Rust Cohle offers a different - and entirely reversed - set of meanings for "light" and "darkness." Darkness - a deeper, darker, warmer darkness than mere unconsciousness - seemed to enfold him peacefully, and he felt surrounded by the love of his deceased small daughter. He "let go," hoping to stay in this darkness, but then he woke up. Back to the light.
This speech and its proximity to the final sentences indicate a smart equivocation - with one voice, "light" and "darkness" have their everyday connotations; with another, they are flipped. The latter voice, consonant with Rust Cohle's earlier presentation of his philosophy, also seems consonant with having just visited the worst basement in literature since Cormac McCarthy's The Road, from which basement, like McCarthy's, no one was rescued.
(Originally published by me at http://pastebin.com/PAUBHAct)