Study the works of any great writer and you'll discover a variety of styles and subjects, but one common thread links them all. It's the uncertainty of outcome and it's a technique used to devastating effect by every popular writer, from Shakespeare to Bronte to Dickens. Why? Because it retains the reader's interest and gives their work pageturner appeal. Will Othello really kill Desdemona? And should Heathcliff really venture on to that windswept and unforgiving moor without at least buttoning up his coat first?

It's not knowing the answers to these burning questions that keeps the reader wanting more. Even contemporary writers such as JK Rowling realise that if you crank up the suspense you'll have small children sleeping in the doorways of bookshops at midnight.

Of course, Hollywood has always known the value of suspense. Its blockbuster storylines of intrigue and suspense only ever unravel in the final moments of the last reel. Even now I can vividly recall the shock and horror when I realised that Bambi's mother had been brutally slain. I almost choked on my sherbert dip. Uncertainty of outcome is what keeps us glued to the screen and on the edge of our seat. A cliffhanger in a TV series has us craving the next episode. A story with an underdog has us watching with bated breath to see if they triumph.

Uncertainty of outcome is central to entertainment. It's at the heart of what we enjoy and, perhaps more importantly, it's central to business - it's what gives us the buzz. If we all knew what would happen when we made business decisions there would be no thrill. And, of course, 'intent' should not be confused with outcome because the surprise factor simply isn't there.

But what of business relationships? They're not about uncertainty of outcome - they're about certainty. The only way to cultivate a good business relationship and enhance your reputation is to keep on making promises. And crucially - to keep on keeping them. That way, the only uncertainty for your customer is not knowing how much you are going to surpass their expectations.

Good business relationships are not about promises and veneer. They're about certainty of outcome - with a few nice surprises thrown in for good measure. By all means continue to make the promises you need to make to create demand for your product or service and enable you to charge a premium price. But then focus on surpassing these expectations.

Philip Hesketh is a professional speaker on the psychology of persuasion and author of 'Life's A Game So Fix The Odds'