“Those retailers are simply fated to live in the inflexible world of racks and aisles, where products must obey the uncompromising physics of atoms, not bits. One of those unfortunate rules of corporeal matter is that it cannot transcend time and space. Obviously, a physical item can be in only one place at any given time. For instance, a can of tuna cannot exist simultaneously in multiple categories, even though the interests and browsing paths of each shopper might suggest many: “fish,” “canned food,” “sandwich makings,” “low-fat,” “on sale,” “best-selling,” “back-to-school,” “under $2,” and so on. A physical store cannot be reconfigured on the fly to cater to each customer based on his or her particular interests.”