Probably our pride. We underestimate nature and the world and over-estimate our own abilities. Lust would be a major one, too. I bet many of the people reading this post right now have a porn tab open. Not that that matters, it's more of an issue of cheating on your partner that I find disgusting. We're also pretty selfish, too. There's also our greediness. We can never be completely satisfied because of our love for material things.
Man, I'm depressed now.