One important lesson that we can learn from the IPv6 experience is that it is enormously difficult to change network-layers protocols. Since the 1990s, numerous new network-layers protocols have been trumpeted as the next major revolution for the Internet, but most of these protocols have had limited success to date ...

Indeed, introducing new protocols into the network layer is like replacing the foundation of a house - it is difficult to do without tearing the whole house down or at least relocating the house's residents. On the other hand, the Internet has witnessed rapid deployment of new protocols at the application layer (for instance, instant messaging, peer-to-peer file sharing, audio and video streaming,...). Introducing new application-layer protocols is like adding a new layer of paint to a house - it is relatively easy to do, and if you choose attractive color, the neighborhood will copy you.
[ovvero, magari la nuova applicazione sarà usata dal "popolo della rete", diventando una delle nuove killer application ...]