Day 1 a founder said, “Auth, billing, AI, dashboard simple,” with a six-week demo-day deadline and zero ICP or success metric. By week one, five voices were steering: investor wanted “enterprise-ready,” advisor “freemium,” friend “mobile-first.” We laid horizontal plumbing (multi-tenant, permissions, settings) with no end-to-end value. Week two, compliance arrived (DPA, sub-processors, deletion flows) and invoices stalled (no PO/VAT/billing contact). Trials ghosted because “connect X & Y” actually meant data cleanup and SSO politics. We were shipping fast and proving nothing. We froze 24 hours and rewrote the plan as two lines: Outcome: “A brand-new user reaches first value in 10 minutes.” Metric: “% of new users hitting first value within 7 days.” Everything bent around that. One client-side owner made final calls; a 15% change budget forced micro-SOWs instead of “quick tweaks”; vertical slice first (signup ,connect one source , first automated output , plain-text confirmation) before any dashboard; a strict Definition of Done (acceptance test + analytics event + doc snippet); a dated decision log; and a Week-1 buyer pack (data flow, SSO/RBAC, backups, DPA summary, export/exit, 90-day uptime) plus clean billing (PO, VAT, billing contact). Result at Day 28: nine-minute TTFV on a cold account, two paid pilots, procurement questions cut 80%, and zero scope whiplash. If you build SaaS for others, start with the ten-minute “aha,” then let scope, pricing, and compliance orbit that single gravity well.