The spectacular foyer of Waterstones Bookshop, Cambridge. Each book on the wall has a handwritten recommendation.

Many years ago, at the start of my career in publishing, an old hand told me what, in his opinion, was the only marketing principle that mattered in trade publishing: “people go into bookshops to buy a book. They come out with a book, but it’s almost never the book they went in to buy!”.  That principle certainly works for me, and every bookseller I’ve talked to about it agrees with it. There is an unexpected element in the act of choosing a book.

The implication of such a principle is quite profound. The design of a book jacket is all-important, since it has to catch your eye without you necessarily knowing the author or the title. There has to be enough information on the front and back cover to convince the casual browser that this is the book they always wanted.

But is serendipity a rule for life? Clearly, Mark Forsyth, author of The Unknown Unknown:  Bookshops and the Delight of Not Getting What You Wanted (2014) , thinks so. He claims that internet searching cannot give you true serendipity, because you have to know what you are looking for. Internet dating can only identify a partner for you according to the criteria you supply.

In his excitement, Mr Forsyth goes so far as to link the Buddhist idea of the suppression of desire to browsing in bookshops: it’s only when we ignore our desires we can truly be free. It sounds like a great idea, and it certainly seems to explain a lot of our behaviour in bookshops. But as a rule for life it would be challenging indeed. Imagine going to university and at the start of each day tossing a coin to determine which course you will follow today.

More precisely, what appears to be serendipitous is already based on an algorithm, even if machine learning has not (yet) been involved in the process. When a customer walks into a bookshop, the books displayed on tables or walls are not randomly selected. However unconscious the process by the bookseller, the selection displayed is the result of a matching process of the age, interests, and profile of the book buyer. That book buyer may well have a profile that matches that of the bookseller, which makes it slightly easier, but in neither case is it entirely serendipitous.

The same process takes place when a viewer turns on the TV. Traditional TV channels such as BBC or ITV will provide what appears to be a random choice of programme, but when you, the viewer, turn on your TV at 8pm in the evening (or 8am in the morning), armies of experts have thought long and hard to provide content that matches the presumed profile of the viewer. You may not know what the programme is in advance, but you’re probably going to like it. I’d call it “seeming serendipity” – it appears to be random, but it is not. So, Mr Forsyth, a fascinating argument, and I for one love the displays in bookshops; but I know that real serendipity requires (paradoxically) a lot of searching, to ensure it is quite random.