In decision-making, facts should be distinguished from values. Values influence the decisions by scientists about what kinds of research to do and how to do it. But the norms of science, over time, promote the evolution of increasingly accurate understanding of facts. It is easier to establish facts when observations are repeatable and ostensible. Sustainability decisions usually require assessment of facts in very specific contexts, and that can increase uncertainty. In such cases, deliberation with interested and affected parties can help get the science right and get the right science. When the powerful see their interests threatened by increasing awareness of risks, they often try to slow the emergence of scientific consensus, especially by emphasizing uncertainty.