Growth decisions are only as good as the numbers behind them — and most startups are flying on dashboards nobody trusts. This pillar covers the practical side of data: instrumentation and event tracking, attribution that survives scrutiny, cohort and retention analysis, and the unit economics that determine whether your acquisition engine actually compounds or quietly burns cash. It's written for founders, growth leads, and RevOps teams who need to know their real CAC, payback period, and LTV — not a vanity metric they can't defend in a board meeting.