Imagine you’re buying a used car. The seller says it’s in perfect shape — but would you just take their word for it? Probably not. You’d want an independent mechanic’s report, a record of accidents, maybe a test drive. You trust information only when you know the rules behind it. Financial reports are exactly like that. Every number a company shows you — sales, debts, profits — was put there by people following a set of shared ideas. This chapter is about those shared ideas: the “why” behind the numbers. It’s the rulebook for building the rulebook.