Let me ask you to do something scary: Imagine you're Jeff Bezos and you've just spent the morning studying your retail empire. How do you feel? Do you brim with confidence? Or do you harbor profound, unshakable paranoia about the rivals storming your gates?

I'm betting you're paranoid. Indeed, I suspect your paranoia explains the frenzy of expansion that has gripped Amazon.com Inc. over the past few years, from its new effort to launch Sunday delivery to its move into grocery service to providing instant, face-to-face technical support on the Kindle Fire.

What could Mr. Bezos possibly have to fear? Impermanence. Mr. Bezos is in an industry, retail sales, in which every innovation is instantly pored over and copied, in which (thanks partly to him) margins are constantly driven to zero, and in which customers are governed by passing fancy and whim. Being online confers fantastic advantages to Amazon, but it also comes at a deep cost: Very little about its business is burned into customers' minds.

Hence, frenzy: Amazon is in a race to embed itself into the fabric of world-wide commerce in a way that would make it indispensable to everyone's shopping habits—and to do so before its rivals wise up to its plans.

The Sunday-shipping plan illustrates its M.O. The plan calls for spending every available resource to build a massively imposing shopping platform that rewires the key feature of modern commerce, from servers to shipping to customer service to marketing. Indeed, when you consider many of its recent efforts, including its $600 million contract to store the CIA's data, it is more useful to think of Amazon as a global infrastructure company rather than a shopping site—more like Maersk than Macy's .