The most important thing you can know about a product is whether anyone comes back to it. Not whether someone bought it once, because a single sale can often be made to happen – catch a person at the right moment with the right offer, and they’ll give your product a try. A first purchase tells you that your promotion worked. But it tells you very little about the experience your product gives people.

The second purchase is another matter. Nobody returns to a thing that let them down. When someone buys again (and then again after that), with no campaigns chasing them and no discount pulling them back, that is a strong signal your product is valuable to people. Which makes it curious how little ongoing attention the product itself gets.

One of the most basic marketing models you learn at business school is the four P’s: product, price, place, and promotion. Together they form the “marketing mix.” The idea is both sound and simple. The product is the good or service you sell, the price is what you charge for it, the place is where it can be purchased, and the promotion is how you let people know about it. By working through these aspects, you can create an offering so attractive that people will hand over their hard-earned money for it. Four levers, each meant to be pulled.

But, in practice, one lever has swallowed the rest. When you talk to marketers today, or sit through presentations at industry events, most put their emphasis on promotion – ads, campaigns, communication. The product, meanwhile, has quietly been demoted to a backdrop: the thing you build your messaging on top of, rather than a thing you keep working on.

And it is easy to understand why: promotion is countable. Open your laptop and you can watch the numbers move. You know how many thousands of people have looked at your ads, how many clicked, and how many bought. You will get exact estimates of cost per acquisition and return on investment. The product’s effect is nothing like this. It shows up slowly, somewhere downstream, in a purchase that might happen months later for reasons no dashboard can clearly show. Faced with one lever you can measure now and one you mostly can’t, it is no surprise that effort has shifted to the one you can see. What is hard to count is easy to neglect.

But the choice between promotion and product is not a simple trade-off. The levers might seem interchangeable – just two ingredients in our marketing mix – but they don’t do the same job.

To get someone through the door for the first time, promotion does almost all of the work. An attractive offer, a well-timed message, or a strong campaign can make a person try something new. This is where promotion does the heavy lifting – driving new customers to the business. The product can’t do this job directly. Before I have tried something, the experience it will give me can’t be what makes me try it; that would be circular. The product’s influence on a first purchase is real, but always secondhand – it reaches new customers through reviews, word of mouth, the friend who says it is worth it.

Getting someone to come back inverts the whole thing. A promotion – some kind of trigger – still helps: a reminder, a notification, the logo catching my eye at the right moment. A small signal puts the brand back in front of me. But the bigger impact on repeat purchases comes from the experience the product gave me the last time. If the product experience was good, the reminder just has to jog my memory and I will come back. But if the first purchase was bad, the promotion will have to work really hard to get me back. Spending money on promotion to get me to give you a second chance, when the product experience already disappointed me once, is close to the most expensive thing a business can do.

This is why the promotion-heavy playbook quietly caps your growth. It is built for the first purchase – the door – and the door is the part of the business where spending more reliably gets you more. So that is where the money and the attention go. But a business that only knows how to open the door has to keep buying every customer, over and over, because it never built the thing that brings them back on their own. You pay for acquisition each time, but retention compounds.

Which returns us to where we started. Promotion gets people through the door – it is the main lever for acquiring new customers. But whether they come back depends on what they meet inside. That is the product. If you want repeat customers, that is not a promotion problem to spend your way out of. It is a product you have to be willing to keep making better.