Is the purpose of the cover to sell books, to accurately describe what’s in the book, or to tee up the reader so the book has maximum impact?

The third.

It’s the third because if the book has maximum impact, then word of mouth is created, and word of mouth is what sells your product, not the cover.

Tactically, the cover sells the back cover, the back cover sells the flap and by then you’ve sold the book. If those steps end up selling a book that the purchaser doesn’t like, game over. So you have to be consistent all the way through and end up creating a conversation after the purchase. Books are better at creating conversations than most products (when was the last time you talked about a pool cue), but there’s lots of opportunity here, no matter what you make.

Some ways that a book cover can accomplish its mission:

  • Iconic (because iconic items tend to signal ‘important’)
  • Noticeable across the room (you see that lots of other people own it, thus making it likely that you’ll want to know why)
  • Sophisticated (because this helps reinforce that the ideas inside are worthy of your time)
  • Original (why bother reading a book you already know)
  • Clever
  • Funny
  • Generic (reminding you of a genre or another book you liked, not generic as in boring)

The purpose of a book cover is not to perfectly illustrate the story down to the smallest detail or to showcase every aspect and facet of the plot. If you think this way, you are too close to your project, and you are thinking about your cover too literal—especially in the digital world where books are bought primarily online and the presentation of the cover has changed from a beautiful piece of art to a small 100 pixel-wide thumbnail.

The sole purpose of a book cover is to help sell the book

A book cover is a selling tool! Nothing more, nothing less. It serves the purpose to attract eyeballs and then get those people intrigued enough to click on the cover thumbnail and learn more about the book, which, hopefully, will then result in a sale.