Why is Amazon so far ahead? It is difficult to resist marveling at the way Mr. Bezos has built his indomitable shopping machine, and the very real advantages in price and convenience that he has brought to America’s national pastime of buying stuff. What has been key to this rise, and missing from many of his competitors’ efforts, is patience. In a very old-fashioned manner, one that is far out of step with a corporate world in which milestones are measured every three months, Amazon has been willing to build its empire methodically and at great cost over almost two decades, despite skepticism from many sectors of the business world.

Image Credit... Stuart Goldenberg

Now those investments are beginning to bear fruit. It’s happening in fulfillment, which is the business term for filling and shipping orders. Amazon has built more than 100 warehouses from which to package and ship goods, and it hasn’t really slowed its pace in establishing more. Because the warehouses speed up Amazon’s shipping, encouraging more shopping, the costs of these centers is becoming an ever-smaller fraction of Amazon’s operations.

Amazon’s investments in Prime, the $99-a-year service that offers free two-day shipping, are also paying off. Last year Mr. Bezos told me that people were increasingly signing up for Prime for the company’s media offerings — the free TV shows, music and movies that come with the subscription, and which Amazon has been spending vast sums to produce.

Mr. Schachter, of Macquarie Securities, estimates that there will be at least 40 million Prime subscribers by the end of this year, and perhaps as many as 60 million, up from an estimated 30 million at the beginning of 2015. He argued that Amazon’s investments in giveaways will help make Prime more attractive to people in lower-income groups. As a result, he predicted that by 2020, 50 percent of American households will have joined Prime, “and that’s very conservative,” he said.

Growth in Prime subscriptions matters because Prime alters the psychology of shopping. Once you’ve prepaid for shipping, you tend to start more of your shopping excursions at Amazon. According to some estimates, people spend three or four times as much with Amazon after they sign up to Prime.

Because Amazon is still expanding madly, its expenses remain enormous and its retail profits tiny. In its last quarter, its operating margin on the North American retail business was 3.5 percent, while Amazon Web Services’s margin was 25 percent.

But this “Prime effect” is key to Amazon’s long-term profitability. Analysts at Morgan Stanley reported recently that “retail gross profit dollars per customer” — a fancy way of measuring how much Amazon makes from each shopper — has accelerated in each of the last four quarters, in part because of Prime. Amazon keeps winning “a larger share of customers’ wallets,” the firm said, eventually “leading to a period of sustained, rising profitability.”