It's Prime Day! Amazon will do tens of billions in sales over 72 hours, a huge chunk of it pulled forward by the event itself. Every ecommerce founder probably felt the same pull: we should be running something too.

But we need to be careful. The thing that makes Prime Day work for Amazon is the thing most brands don't have.

Here's the behavioral idea for my thought - we don't judge a price against its true value. We judge it against the price we expected to pay. Economists call it the reference price.

A $40 shirt feels like a steal if it was $80, and like a ripoff if it was $30 last week. The number on the tag matters less than the number already in your customer's head.

Amazon can move that reference point for two days and then move it back, because it has billions of buyers, infinite selection, and no single brand relationship to damage. The discount creates new demand.

Most brands aren't Amazon. When a smaller brand runs 20% off every few weeks, it doesn't just lose 20% margin on that sale. It resets the reference price in its customers' heads. Full price starts to feel like a punishment. And customers quietly learn to wait for the next drop.

JCPenney ran the most expensive version of this lesson in retail history. In 2012, a new CEO killed the constant coupons and 'fake' sale prices, and switched to honest everyday low pricing.

Sounds good, right? Sales fell about 25% in a year!!

People didn't [always] want low prices. They wanted to feel like they'd won. The CEO's own postmortem: 'Coupons were a drug. They really drove traffic.'

Now, this is a two-sided trap. If you discount constantly and you train your customers to wait. Take the discounts away and the withdrawal is brutal.

So, this Prime Day, before any of us copy the playbook, we should ask what our promo is actually doing. Pulling forward a sale that wasn't going to happen? Or just discounting one that was, while teaching your customer to hold out next time?

Tentpole events (Black Friday, and yes, your own Prime-Day-timed sale) can be worth running for competitive reasons. But a promo should change behavior, not just reward the behavior you already had.