The rule of threes is famous in survival circles — I’ve written about it before — but now I want to narrow in on what is usually the top priority. You can go three minutes without air, three hours without shelter, three days without water, and three weeks without food. Talking about air would be silly, so this article is about shelter. I’m not going to teach you how to build a shelter in this lesson. Instead, I’m going to talk about what qualifies as a shelter.