Sectus's law (also known as Sectus's Rule of Brony Analogies or Sectus's Law of Brony Analogies) is an argument made by Sectus in 2011. It states: "As an online discussion grows longer, the probability of a topic involving bronies or MLP:FiM approaches 1." In other words, Sectus observed that, given enough time, in any online discussion-regardless of topic or scope-someone inevitably makes a post involving bronies or MLP:FiM.
This law can be applied to any and all forums, discussions, and topics, regardless of their nature or original intent. No matter what, as long as a conversation exists, it holds the possibility of dissolving into a heavily brony-laden flame war.