What product market fit measures
It measures whether a defined group of people wants what you sell strongly enough to buy it, keep it, and tell others. The important word is evidence. Compliments, sign-ups and encouraging conversations are not evidence; repeat purchase, low churn, referrals and buyers who resist being taken off the product are.
The signals differ by business model. For a subscription, watch retention and how quickly cancelled customers come back. For a service business, watch renewal, referral and whether clients bring you second projects without a pitch. For a shop, watch repeat orders and whether people return without a discount pulling them in.
There is a softer signal worth taking seriously: how disappointed existing customers say they would be if the offer disappeared. Asked properly, and asked only of people who have genuinely used it, that question separates polite interest from real dependence.
Why product market fit matters
Because marketing multiplies whatever is already there. Without fit, spending harder simply fills the top of the marketing funnel with people who leave again, and every channel looks broken in turn: ads too dear, SEO too slow, email ignored. The pattern is usually one problem in different costumes.
With fit, the same spending compounds. Customers stay long enough to pay back their acquisition cost, they recommend you, and the reviews and word of mouth make paid channels cheaper over time. That is why it is worth deciding honestly which situation you are in before setting a budget.
Common mistakes with product market fit
The first is treating it as a single moment. Fit exists for a specific offer, a specific type of buyer and a specific market. Selling the same service into a new country, or to much larger clients, means finding it again from a standing start.
The second is reading survivor evidence only. If you count the customers who stayed and never ask the ones who left, everything looks healthy. The leavers hold the information you need, and a short, direct question at cancellation usually gets an honest answer.
The third is buying fit with discounts. Deep discounting produces purchases from people who wanted a bargain, not the product, and the numbers look like traction until the offer ends.
How to act on it
If the evidence is weak, stop scaling and narrow instead. Pick the segment where results are strongest, rewrite the offer around that group, and accept a smaller market that actually converts. Narrowing is cheaper than advertising your way past a mismatch.
If the evidence is strong, the job changes to reaching more of the same people without diluting what worked, which is the point at which marketing strategy consulting earns its keep. Either way, decide with retention and repeat behaviour in front of you, not with a chart of first-time visits.