In the beginning was the image. A spellbinding, captivating sight -- one so extraordinary on Dhaka's streets that I am already wondering if it wasn't a trick of the light, an optical illusion, a fanciful epiphany.

I was sitting in my car on the way to work down one of the city's wide avenues. Half-concentrating on my book, half-trying to block out the brass band of fifty types of car horn. By chance I glanced up and across the street, attracted perhaps by a sudden movement, as of a tropical bird darting into flight. The other side of the road at first seemed unusually quiet. Then I saw her, right in the middle. Her arms were outstretched and she seemed to be gliding. It took a moment to realise that this was a powerful young woman actually roller-blading down the road: a pure symbol of grace, freedom and movement. Her face was striking in the morning light, against the blurred background of trees. I recall her scarlet tracksuit, her hair daubed with a gleam of creamy sun and the fact that she was smiling with utter exhilaration. But before I could drink in any more details, the traffic on my side closed in and swept us along like a swarm of hornets, and the image was lost for ever.

Or was it? I thought no more of it, until later that week I heard a muffled knocking in my skull. It slowly became clear that in a moment when my concentration lapsed, this magical girl had actually slipped in to my head and was now captive there. But she was soon plaintively dissatisfied with this narrow imprisonment, pleading for release, like a princess in a mediaeval tower. And at that moment I understood I had to free her in the only way I knew: through putting her on a page.

Why bother? Why not put in some earplugs, leave her locked up and let her languish in there, fading slowly into oblivion?

I can think of some very good reasons why. First, a realisation that in a rapidly-changing world, these moments of extraordinary significance need to be held on to. They cannot be allowed to slip away. For too many years I did that, and now thousands of such images lie buried in the rubble of my past.

But then the challenge arises of how to convey these images in words. The problem is, there are so many damn words around -- which ones to choose? The art, I suppose, lies in emulating the sculptor who sees the statue inside the stone, and simply works to liberate it. And so, from the vast body of words in the lexicon, the trick is to eliminate all the useless ones, the false leads, the vain, pompous and purple, and to allow just the right ones to remain. Not an easy feat. Each time the initial written description is re-read minute changes are made. The final product emerges only slowly, and tentatively, until the words seem, to your eyes at least, to have assumed their rightful and final resting place.

There is also of course the thorny question of recall -- how reliable is the image now floating in front of my eyes? I can hardly depend on my tricksy memory: I have returned to too many cities looking for exactly that graceful mosque and golden fountain which adjoined each other so clearly together in my mind, only to find they occupied different streets altogether. Perhaps if that skating moment had been caught on video camera, I would be wrong in almost every detail. But this doesn't matter: what matters is that she was there. She was a spark, a catalyst, though she herself is of course blissfully unaware of the subsequent chain of events in my head.

Besides, the image that remains with me now has as much right to life as the original reality. Creative writing means working with these raw materials and crafting them so that their essence and their beauty can emerge, not documenting them microscopically like some scribbling clerk.

And as you do so, you cause others to be inspired or moved, to laugh, weep or close their eyes in silent remembrance. Here is our second reason: writing allows us to share. Each of us has access to unique experiences which can be relayed to others or remain locked in our own minds, but what good can they do there? I want you to treasure this image too. And in return I beg for those remarkable tableaux which you have squirreled away. Let's have 'em: they're too good to hide in a drawer, or leave in the dusty corridors of our own heads.

Of course, if I'm honest, there may also be a third reason for this urge to write. Is it just about capturing and sharing moments of note, or is the writer also driven by the tempting idea of leaving something to posterity -- a modest memorial inscribed with the epitaph: “I was here. I existed”? Perhaps there is a little of that: we have precious little else to comfort us when set against the certain knowledge that we will die, be remembered for a while, then disappear for ever from living memory. Who now recalls your grandfather's grandfather?

Maybe we should also acknowledge our sense of pleasure that what we write will be read by others, that we have an audience. There may be a few driven souls out there whose writing exists for themselves alone, but for many the relationship to a readership is vital. Our writing needs to be read. If you were the last person on earth, would you still want to write?

But for now, there are still plenty of people around, still legions of readers to reach. So waste no time. Look around, (writing can make you a better observer too), drink in the vivid details of what you see, use your every sense, and start to create. These moments which are too important to let slip, too precious to hoard to yourself. Find a quiet place, let your pen hover over the page, breathe deeply, and begin.

Andrew Morris is an expatriate British writer living in Dhaka.