Petyr Baelish: When boys and girls live in the same home, awkward situations can arise. Sometimes, I've heard, even brothers and sisters develop certain affections. And when these affections become common knowledge, well... that is an awkward situation indeed, especially in a prominent family. But prominent families often forget a simple truth, I've found.

Cersei Lannister: And which truth is that?

Petyr Baelish: Knowledge is power.