More than 90 years ago, holiday shopping found its official start the Friday after Thanksgiving, eventually becoming Black Friday, the biggest shopping day of the year. Over the years, Amazon has helped make Black Friday even more of a global online shopping phenomenon. Next week, Amazon turns 20 and on the eve of its birthday, the company introduces Prime Day, a global shopping event, offering more deals than Black Friday, exclusively for Prime members in the U.S., U.K., Spain, Japan, Italy, Germany, France, Canada and Austria. On Wednesday, July 15, new and existing members in the U.S. will find deals starting at midnight, with new deals starting as often as every ten minutes. They can shop thousands of Lightning Deals, seven popular Deals of the Day and receive unlimited fast, free shipping. Not a Prime member? To participate in Prime Day, Amazon customers can sign up for a 30-day free trial of Prime at amazon.com/primeday.

Amazon is creating its own shopping holiday. Economists and retailers have long debated what would happen if there were two Christmases a year instead of one. Would that just move consumer spending around or would it increase the share of the pie? Amazon doesn't have to worry about that here because they're just focused on their own revenue, and if this shifts retail spending share to them, all is good.

It can be dangerous for a retailer to become dependent on sales, but Amazon is a special case. Restoration Hardware has a twice a year sale on its towels, also on its lighting. Customers feel a bit silly buying those items from them any other time of year. Criterion DVDs go on sale at 50% off from time to time. To buy one at any lower discount feels like you're leaving money on the table.

Amazon has such a large catalog of items, and the items it puts on sale are so random, that it's immune to creating artificial seasonality with its sales. Its customers buy from them so often that it's not practical to wait until items go on sale to shop there.

Besides, the core of Amazon's value is everyday low pricing, so most customers feel like they're getting a great deal on most everything purchased there anyhow. A bunch of random deals on Prime Day are just gravy. And if this goes off well and becomes an annual occurrence, it may drive more people to join Amazon Prime, even better for Amazon because of the loyal customers Prime memberships create and the increase in shopping volume and frequency from that cohort.