What distinguishes a great mnemonist, I learned, is the ability to create lavish images on the fly, to paint in the mind a scene so unlike any other it cannot be forgotten. And to do it quickly. Many competitive mnemonists argue that their skills are less a feat of memory than of creativity.

Once upon a time, this idea of having a trained, disciplined, cultivated memory was not nearly so alien as it would seem to us to be today.

If you want to make information stick, it's best to learn it, go away from it for a while, come back to it later, leave it behind again, and once again return to it - to engage with it deeply across time. Our memories naturally degrade, but each time you return to a memory, you reactivate its neural network and help to lock it in.

With our blogs and tweets, digital cameras, and unlimited-gigabyte e-mail archives, participation in the online culture now means creating a trail of always present, ever searchable, unforgetting external memories that only grows as one ages.

All across Africa, the Pacific and the Americas, we find cultures that didn't know about mouth kissing until their first contact with European explorers. And the attraction was not always immediately apparent. Most considered the act of exchanging saliva revolting.

To improve, we must watch ourselves fail, and learn from our mistakes.

We're all just a bundle of habits shaped by our memories. And to the extent that we control our lives, we do so by gradually altering those habits, which is to say the networks of our memory. No lasting joke, or invention, or insight, or work of art was ever produced by an external memory. Not yet, at least.