If you want to live a memorable life, you have to be the kind of person who remembers to remember.

Monotony collapses time; novelty unfolds it. You can exercise daily and eat healthily and live a long life, while experiencing a short one. If you spend your life sitting in a cubicle and passing papers, one day is bound to blend unmemorably into the next - and disappear.

We've outsourced our memories to digital devices, and the result is that we no longer trust our memories. We see every small forgotten thing as evidence that they're failing us.

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.

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.

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.

Some memorizers arbitrarily associate each playing card with a familiar person or object, so that the king of clubs is represented by, say, Tony Danza. The grand masters associate each card with a person, an action, or an object so that every group of three cards can be converted into a sentence.