Most startups fail not because the team couldn't build the product, but because nobody wanted it. Validation is the discipline of finding that out before you spend a year and your savings building the wrong thing.
Start with the problem, not the solution. Talk to at least twenty people who live with the problem you want to solve. Ask what they do today, what it costs them, and what they've already tried. If they aren't actively looking for a fix, the pain probably isn't sharp enough to build a business on.
Next, size the opportunity. A real market has enough reachable customers who can pay. Estimate your TAM, SAM and SOM with real numbers, and study who already serves this market — direct competitors validate demand, and their weaknesses are your opening.
Finally, test willingness to pay before you build. A landing page, a pre-order, or a paid pilot tells you more than a hundred "that's a great idea" comments. AI tools like XpertVex compress weeks of this research into minutes, giving you a grounded viability score and the sources behind it — but the principle is timeless: evidence beats opinion.