PMF: You Know It When You See It
On defining product-market fit, and knowing when you’re close.
A founder asked me recently how to know when they’ve found product-market fit. It’s a question I hear a lot, and while there are all kinds of frameworks out there, the most useful one I can offer is borrowed from Justice Potter Stewart, who was trying to define obscenity: “I know it when I see it.”
It’s not a cop-out. It’s a reflection of how slippery PMF can be in practice, and how founders often try to codify something that’s more diagnostic than definitional.
There are patterns, though. When you’re close to product-market fit:
You don’t need to brute-force the top of the funnel with mass outbound.
Sales cycles compress, feedback loops tighten.
Buyer personas stop needing nudges and start championing internally, because the solution actually solves something real.
Instead of dragging leads over the line, you find yourself catching up to inbound. The questions change from “why do we need this?” to “why didn’t someone build this sooner?”
Or as Marc Andreessen put it: “The market pulls the product out of your hands.”
That’s the moment I most enjoy with companies: when they’re right on the cusp. Some traction, yes, but still messy enough that support actually matters.
Most of the founders I back are solving real problems. Pain pills, not vitamins. They’re building for customers who really, actually need the product, not just admire it conceptually. And when that’s true, the signals are there if you know what to look for. You’ll see usage patterns that defy your initial assumptions. You’ll lose a deal and still get a thank-you note. You’ll wake up to a calendar full of prospects who found you.
But getting to that point requires discipline. I’ve seen companies stall for quarters because they couldn’t stop selling the version of the pitch they wanted to be true, rather than the one the market was reacting to. The best founders I’ve worked with treat GTM as a discovery process. They adjust the frame until it snaps into place.
That doesn’t mean chasing every shiny logo, especially if that prospect would require some large custom build-out that isn’t universally applicable. It means having enough clarity to recognize what’s working, and enough conviction to focus there, and iterating until you feel the subtle infection point.
So if you’re wondering whether you’ve found product-market fit, ask yourself this:
Are prospects repeating your value prop back to you in their own words?
Are you closing faster than before, without steep discounts or heroics?
Are users showing up without needing to be reminded?
Are you hearing “this is exactly what we needed” more than “we’ll think about it”?
Want a metric? Sean Ellis’s 40% test is a good one: if you survey your users and 40%+ say they’d be ‘very disappointed’ if the product disappeared, you’re probably in the zone.
It’s not scientific. It’s not even linear. But when it clicks, it clicks. That’s the moment to double down: lock the narrative, focus the roadmap, and pull the team into alignment. Don’t chase every shiny use case. Don’t overhire. Just feed what’s already working, and clear everything else out of the way.
I’ve seen that moment up close, with teams solving real problems for customers who can’t wait. It’s what I look for now when meeting early-stage founders. You can’t fake it. But if you’re close, you can usually feel it.
And like Justice Stewart said: you know it when you see it.