Here’s a basic truth about people who make decisions about public policy: they rarely have all the facts they want. Yet policy has to get made anyway.

No one is confronted more often with this conundrum than the President of the United States, though members of Congress can come close. The challenge is that purported facts are dynamic — they keep changing. Additional facts come to light. Others are found to be wrong. Some are clearly reliable, others more dubious. And regardless, they come at high-level policy makers quickly, relentlessly, from all directions, and from all kinds of sources.