It's a weird paradox. Despite management's obsession with hard numbers, many organisations are a fact-free zone, swirling with untested assumptions. Horrifying sums of money are committed on superstition or whim. Thus, fact-based management is really triple-distilled common sense. It's hard. It requires judgment, practice, help, humanity and wisdom. It needs scepticism and experimentation. It needs reasoned optimism and learning, and, as F Scott Fitzgerald put it, the ability to function while holding two contradictory ideas in your head at the same time.