Perhaps it's due to the fact that TV Tropes' mission is essentially to perform inference on the entire body of human fiction, and create generalised models (tropes or trope complexes) from that data. In many ways, it's science applied to things that are made up!
This is our monthly thread for collecting these little gems and pearls of wisdom, rationality-related quotes you've seen recently, or had stored in your quotesfile for ages, and which might be handy to link to in one of our discussions.