The title How To Win Friends and Influence People reeks of insincerity. How many people would boast of 'winning' a friend and influencing them for their own personal gain? It just doesn't sound nice. For a modern reader, the book conjures up mental trickery for a dog-eat-dog world, a shonky product hawked by a Depression-era salesman. In this case, judging a book by its cover would seem a very reasonable thing to do.

Yet the reader should consider some points in the book's defence.

First, there is a strange inconsistency between the brazenness of the title and much of what is actually in the book. When read carefully, it is not at all a manual for manipulation, in the manner of Machiavelli's The Prince . Carnegie genuinely despised 'winning friends' for a purpose. The energy which makes the book a great read comes from a love of people.

Second, Carnegie wrote it in the America of the 1930s. The country was still clawing itself out of the Great Depression, and opportunities, particularly for people with limited education, were scarce. Carnegie offered a way to get ahead, taking advantage of the one thing you truly owned outright - your personality. By modern standards, the claims made in How To Win Friends do not seem too wild - motivational psychology is now well established. But try to imagine its impact in 1937, before the great prosperity of the post-World War Two period. To many people it would have seemed liked gold.

Third, the book was not written with an eye to bestseller glory, being a textbook for Carnegie's courses in Effective Speaking and Human Relations (the 'How to' part of the title is a giveaway as to its course origin). The initial print run was only 5,000 copies. Rather than being devised as part of some masterplan to profit from people's baser instincts, the aim was to bring the messages of the Carnegie courses to a reading audience.

But the book, initially no doubt due to the title alone, caused a sensation. It is one of the biggest selling books ever (over 15 million copies, in all the world's main languages), and still the biggest overall seller in the self-improvement field. In her preface to the 1981 edition, Dorothy Carnegie notes how her husband's ideas filled a real need that was 'more than a faddish phenomenon of post-Depression days'. Indeed, How To Win Friends is written up in compendiums like Most Significant Books of the 20th century , and takes its place in Crainer & Hamel's Ultimate Business Library: 50 Books That Made Management , among titles by Henry Ford, Adam Smith, Max Weber and Peter Drucker.

The book lists 27 principles, but you will have to get a copy to appreciate them in their context.

Though it is easy to parody, the book itself is genuinely funny - quite a rare thing in personal development writing. If it had simply been a compendium of old wisdom, new findings and anecdotes, the book would have still been worth reading, but dry. It took Carnegie's log cabin sense of humour to make it a text that really pulled you in. One of its famous principles is Remember that a person's name is to that person the sweetest and most important sound in any language.

How To Win Friends was a revolutionary book because it put firmly into the public's mind that human relations are more understandable than we think, and that people skills can be systematically learned. It also proposed that we don't truly influence a person until we like and respect them first.