When your first users sign up but never return, it's a clear signal of a problem-solution mismatch. Before abandoning the idea, you must interview these users to understand why. Their feedback is crucial data needed to decide whether to iterate or pivot.

Vanity metrics like total revenue can be misleading. A startup might acquire many low-priced, low-usage customers without solving a core problem. Deep, consistent user engagement statistics are a much stronger indicator of genuine, 'found' demand than top-line numbers alone.

Founders who've already built a product haven't missed the 'validation' window. The focus simply shifts from 'is there a problem?' to de-risking subsequent assumptions: Is the solution worthwhile? Will people pay enough? Can customers be acquired profitably? This process is ongoing, even at scale.

Many founders mistakenly define Product-Market Fit by revenue (e.g., "$1M ARR"). The correct measure is the ability to predictably create customer value. This is best quantified by a leading indicator for long-term retention, not sales figures, as revenue can be achieved without true market fit.

The true indicator of Product-Market Fit isn't how fast you can sign up new users, but how effectively you can retain them. High growth with high churn is a false signal that leads to a plateau, not compounding growth.

Don't treat validation as a one-off task before development. The most successful products maintain a constant feedback loop with users to adapt to changing needs, regulations, and tastes. The worst mistake is to stop listening after the initial launch, as businesses that fail to adapt ultimately fail.

The ultimate test of PMF isn't surveys or usage metrics, but how indispensable your product is. If customers don't immediately notice and complain when it's gone, you haven't achieved true dependency. It's a visceral, high-signal test for any founder.

Hux's founder measures success not just by retention, but by the passion of retained users. When users start writing in daily, angrily demanding bug fixes, it's a strong positive signal. It means the product has become so essential to their routine that they care deeply about its improvement.

Sales are a vanity metric for product-market fit. The real test is having ~25 customers who have successfully implemented your product and achieved the specific ROI promised during the sales process. If you don't have this, you have a product problem, not a go-to-market problem.