The PRD step exists so “idea → live product” stays honest. Before the agent spends tokens rewriting large parts of the tree, you confirm what success looks like: audience, must-have features, and what can wait.
That alignment reduces thrash. Founders get fewer mismatches between what they imagined and what shipped, and the workspace chat stays focused on execution instead of re-negotiating scope every message.
You can always revisit the brief as you learn, but the default path treats the PRD as the contract for the first vertical slice. It is one of the ways Motivd keeps AI-generated software accountable to a human brief.