21. Why participate … people have social reasons to participate on social network sites, and these social motivations explain both why users value Facebook notwithstanding its well-known privacy risks and why they systematically underestimate those risks . Facebook provides users with a forum in which they can craft social identities , forge reciprocal relationships, and accumulate social capital. These are important, even primal, human desires, whose immediacy can trigger systematic biases in the mechanisms people use to valuate privacy risks. (Grimmelmann 2008)