I'm a great admirer of people who can come up with vivid analogies to explain stuff. In this particular case, the 'stuff' is not all that difficult, but still, Carr has a pretty neat analogy to explain the feeding of long-term memory, and how the intertubes derail that process:
The depth of our intelligence hinges on our ability to transfer information from working memory, the scratch pad of consciousness, to long-term memory, the mind’s filing system. When facts and experiences enter our long-term memory, we are able to weave them into the complex ideas that give richness to our thought. But the passage from working memory to long-term memory also forms a bottleneck in our brain. Whereas long-term memory has an almost unlimited capacity, working memory can hold only a relatively small amount of information at a time. And that short-term storage is fragile: A break in our attention can sweep its contents from our mind.
Imagine filling a bathtub with a thimble; that’s the challenge involved in moving information from working memory into long-term memory. When we read a book, the information faucet provides a steady drip, which we can control by varying the pace of our reading. Through our single-minded concentration on the text, we can transfer much of the information, thimbleful by thimbleful, into long-term memory and forge the rich associations essential to the creation of knowledge and wisdom.
On the Net, we face many information faucets, all going full blast. Our little thimble overflows as we rush from tap to tap. [...]