Metrics tell you how your business is doing. Core: MRR (monthly recurring revenue), ARR (annual), churn, LTV (lifetime value), CAC (customer acquisition cost).
Goal metrics: LTV:CAC ratio > 3:1, payback period under 12 months, churn under 5% monthly. Track in a dashboard—weekly review keeps you honest.
vanity metrics: downloads, signups, page views don't pay bills. Revenue, retention, expansion matter. If you're not measuring, you're guessing.