How do I validate a startup idea before building it?

Friends saying 'great idea' is noise — they're pricing your friendship, not your product. Validation = evidence someone will PAY or ACT, gathered before you build: 1. The Mom Test rule: never pitch, only ask about their life. 'How do you handle X today? When did it last hurt? What have you tried?' Past behavior is data; opinions about your future product are not. 2. Find the workaround: people with real problems have duct-tape solutions (spreadsheets, WhatsApp groups, hired help). No workaround usually means no real pain. 3. Sell before building: a landing page describing the product + a 'request access / pre-order' button + ₹500 deposits or signed LOIs for B2B. Ten strangers paying anything beats a thousand 'would you use this?' yeses. 4. Do it manually first: deliver the service by hand to 5 customers (concierge MVP). You'll learn what the product must actually do — and you'll have revenue. Budget two of your twelve weeks for this. The expensive failure isn't building wrong — it's building unwanted.