Core Principles
Unvalidated Decisions Are Toxic Inventory
Decisions you haven't tested yet accumulate like debt.
Alistair Cockburn's key insight: decisions you haven't tested yet accumulate like debt. Pre-specification documents (PRDs, detailed requirements) are full of stacked, unvalidated decisions. They're betting the entire roadmap on assumptions that haven't been questioned.
LDD minimizes this inventory by validating assumptions as early and often as possible. A thin slice that tests one core hypothesis is worth more than a 50-page spec that assumes ten things.