I belong to a writers club in my town. Its monthly meeting attracts as many as 60 members, depending on the subject of the main talk and the notoriety of the speaker. Prior to the main meeting there is a meeting of the marketing group. It meets for an hour and attracts about half as many people.

The marketing group has its regular participants and its occasional participants. All of them are anxious to learn how to let more prospective customers know about their books. Most participants have a single book to their names. A few have half a dozen or more, and others are still working on their first books.

Clubs such as this one attract writers of varying skills and experience. Some actually are good writers. Some have had modest success in marketing their books. Most are in no danger of winning literary prizes and are surprised when their monthly unit sales reach double digits. Occasionally a writer will report on a book signing event at a book store. Some around the table will perk up at the mention of five or ten copies being sold. For them, that would be a windfall.

I confess I remain surprised at how few attendees appreciate the role of their books’ covers. They don’t seem to understand that the book cover has taken on a new function in the age of digital books: the cover now is a book’s chief marketing tool, eclipsing all else. Even people who prefer to make their purchases at brick-and-mortar book stores commonly discover the books they want online, and all those who no longer frequent book stores (the majority of purchasers) find what they want at Amazon or similar sites.

At a book store, a buyer might pick up a book with a ho-hum cover simply because he’s standing in front of the shelf where that book resides. He may not be impressed by the front cover, but he might find something on the back cover to keep his attention. He can flip through the pages. He can heft the book. He can look at the cover from several angles, and he just might buy the book, even if its cover otherwise displeases him.

That same buyer, sitting before his computer at home, operates differently. In a few minutes dozens or even hundreds of book covers pass before his eyes, once he visits an online seller. Each cover will be the same small size. The books may be grouped for him by genre or author, but otherwise he is on his own.

His eyes pass from one cover to the next, lingering only a second or two, until a cover captures his attention. He clicks on it and is taken to a page touting the book’s virtues, the author’s skills, and the low price, as least as compared to the print version. He sees a long or short description of the book. He is unable to flip through the pages in a tactile way, and he may have to click on the print edition to see the back-cover blurbs, but he gleans enough information about the book to make a decision.

What is it about a book’s cover that captures the buyer’s attention? An interesting graphic treatment, an intriguing title, text that is legible, an overall style that indicates the book’s genre—those are things the buyer reacts to even if not quite consciously. He “likes” the cover, even if he wouldn’t be able to explain just why.

If a cover doesn’t attract him, he doesn’t click through to that book, perhaps to his loss. It might have been precisely the book he was hoping to find, but he won’t know because he won’t get to the first page. He won’t see the author’s words because he won’t get past the cover.

In the early days of printing, from Gutenberg onward, a cover’s chief role was to protect the pages from the elements. Not until the twentieth century, with the advent of dust jackets, was there much room for artistry on covers. Before then, covers were noted for their leatherwork or binding, but they did little to attract purchasers who otherwise hadn’t been looking for those particular volumes.

(I have a forty-volume set of the collected works of John Henry Newman, published by multiple publishing houses over a several-year span in the 1870s and 1880s. The leather covers are wonderfully designed, with raised ribs and gilt lettering. They are among the handsomest books I’ve ever seen, but those covers were not marketing devices per se.)

Paperbacks didn’t come into wide use until after World War II. In parallel with the general expansion of advertising, their covers became tools to foster sales, though few early paperbacks sported covers that could be called first-rate designs. Over the succeeding decades paperback covers improved only slowly, perhaps understandably so, since nearly all books were purchased in book stores, where they could be held in the hand and considered at leisure.

Then came online book stores and self-publishing. Competition for eyeballs became intense—and remains so. Throughout the era of paperback domination and, before that, of hardbacks, advertising for books largely was independent of the books themselves. There were ads in newspapers, magazines, and, of course, catalogues, but all that largely has disappeared. Display ads once turned a profit for publishers. They long have ceased to do so. Today the dynamics are different, which means the purpose of covers is different.

I hope over time to find ways to impress upon members of my writers club that they need to become as serious about their books’ covers as they are about their books’ words. Not just that: I want to impress upon them that, while they might occasionally use other means of promotion, such as book signings, their sales chiefly will come—if they come at all—as a consequence of buyers seeing their covers and delighting in them.

Two and a half centuries ago Samuel Johnson quipped that “No man but a blockhead ever wrote, except for money.” In his case—at least until he received a pension from the King—that literally was true. If Johnson didn’t write, he didn’t eat. But not everyone then or now writes for money. Some people just want to see their words enshrined in print, and they don’t much care whether anyone else ever reads what they wrote.

But most writers, even the most inexperienced, hope to have a wide readership. That requires wide sales, and nowadays wide sales require fine covers. That’s just the way it is.