Sometime last summer, a quarter-billion dollars went missing at Amazon.

Analysts were expecting the usual gangbusters third quarter. But it was about $250 million short of forecasts.

Here is one way to look at the disappointing results: Amazon, for all its heft, is starting to lose momentum. It was rejected by some customers who were put off by its acrimonious dispute with the publisher Hachette over e-books, while others found its prices less compelling than they once were.

But few things about the retailer are ever clear-cut, so here is another interpretation: Amazon is intentionally cannibalizing some major product lines — offering free or nearly free music, video and e-books — to draw tens of millions of people into its ecosystem.

Far from being weak, Amazon in this view is so strong that it is disrupting not only other retailers but also itself, knowingly and eagerly, as it seeks to leverage its powerful e-commerce operation to become a retail and entertainment colossus. It wants to sell devices, entertainment and services as well as basics like milk and toilet paper.