A sale is just the first step. The true measure of product-market fit is high retention, specifically when the product becomes so integrated into a customer's workflow that the idea of canceling their subscription would be bizarre and disruptive. Founders should be designing for this "weird to cancel" status.

The founder realized his product was essential when the customer Slack channel blew up with urgent feedback during their month-end close. This intense, demanding engagement signaled deep user reliance, unlike the 'empty platitudes' from users of a non-essential tool.

With app discovery effectively dead (average zero new downloads/month), Mark Pincus contends that the critical metric is Day 365 retention. Your product's initial experience must convince a user not just to try it, but to envision it as part of their digital life a year later.

"Adoption" can be a superficial metric of initial use. The term "absorption" forces a higher standard, implying a feature has become an indispensable, natural part of a user's regular workflow. This reframing focuses teams on creating lasting behavioral change, not just clicks.

Zynga founder Mark Pincus suggests analyzing a product's Net Promoter Score (NPS) when users quit. If users are proud to stop using your product, similar to quitting cigarettes, it's a major sign of brand weakness and a poor user experience, even if engagement metrics look strong.

To cut through corporate speak about product-market fit, ask a provocative question: 'Will someone use this app while on the toilet?' This forces an honest evaluation of whether a product is compelling enough to capture a user's attention during their most unfiltered, idle moments.

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.

Don't wait for post-launch metrics to validate an idea. The essential evidence for whether to build something is gathered through direct, face-to-face conversations with users about their problems. This pre-build signal is far more reliable than any data collected after shipping.

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.