THE ADVANCES have all been about giving us more detail, more depth. Greater visual richness.

High-definition television, with ultra HD on the way, so that close-ups show every blemish and crooked eyebrow.

Cinema in three dimensions, so we flinch when the roaring sabre-toothed thingummy bursts out of the screen.

Virtual reality headsets promise to transform everything from home entertainment to the operating theatre within a very few years, giving us an experience that’s all-round and completely immersive. Why, you can get your phone to do the job, with the right app and a few bits of cardboard.

But the writer’s job isn’t to put in every last little detail, whether it’s on the page or in the picture. No. We’re making something up, and the reader or viewer is playing ‘Let’s pretend’ with us.

So it’s not about the mass of detail, it’s about picking the right one or two. The ones that really matter. Start with a blank page, the old saying goes, and leave out everything that doesn’t belong.

Think about War Horse, the National Theatre’s hugely successful play, just reaching the end of its second visit to Bradford. The most important character is a horse called Joey, taken from his home on a farm in Devon and plunged into the murderous battlefields of France in the first world war.

It’s a powerful, moving story that deserves every bit of its success and acclaim. And — spoiler alert — he’s not a real horse. Not on stage, at any rate.

He’s a puppet. A puppet that’s bigger than life-size, big enough for flesh-and-blood human actors to saddle him up and ride. It takes three puppeteers to make him move across the stage.

No horse ever looked like this. He has metal ribs, and mesh sides. He has four legs of his own, and four human legs as well, and his hips are wheels.

But no horse was ever so real, either. At the end, in the curtain calls, he gets the biggest cheer from the audience.

Within five minutes we forget we’re watching puppeteers, hardly even see them. It’s called ‘the willing suspension of disbelief.’

The trick is in how the puppeteers select just one or two details, but the exact right ones. The way he’ll crane his neck and toss his head, the way an impatient hoof paws the ground. The way gunshots and loud noises make him skitter and jump.

Everything that’s irrelevant has been left out; what’s left in is what’s most convincing. But the question of what’s relevant and what’s not, now that’s the hard one. The decisions take care, thought, honesty — and, invariably, several unsuccessful drafts before the right one starts to emerge.

Get it wrong and the reader will sigh, put the book down and go make a cup of tea.

Get it right and your horse will fly.