I’ve always heard (and never doubted) that the best, most certain way to sell books is word of mouth: if your friend liked it and recommends it to you, odds are you’ll buy the book they recommended rather than the one next to it on the shelf about which you’ve heard nothing.

And though this principle always made sense to me–you tend to trust the opinions of your friends, and groups of friends tend to be fairly like-minded in their tastes and interests (my friends’ love of the Ottawa Senators notwithstanding)–it really struck home last night when I was reading Pat Rothfuss blog. 

It was because this “word of mouth” principle was put into a striking visual form. See, some fan’s of Pat Rothfuss’ book The Name of the Wind showed up en masse at a book signing and presented Pat Rothfuss with a genealogy of how it came to be that the whole group had read his book.

Yeah, that’s right–a family tree of discovering an author. How cool is that? And how cool are Pat Rothfuss fans!?!? Check out the visual here.

It started with one person. She saw or read something on the internet, picked up the book as a result, and after loving the book (and it’s a good one!) she started spreading the word amongst her friends. From her recommendation to two friends, it looks like at least 26 people read (and looks like most loved, because they kept spreading the word) The Name of the Wind.

What blows my mind is seeing how this meme propagated through this group of friends, and presumably out into other circles that each of these people in the tree are part of. This is the kind of chart an epidemiologist would make up to track an outbreak of ebola or something–tracking back links of contact to a single cause, the Patient Zero. This just blows my mind.

Did all these people buy a copy of Pat Rothfuss’ book? Probably not. They might have borrowed one from the friend who recommended it (I can’t count how many times I’ve thrust a book into my buddy Andre’s arms and said: “You need to read THIS”), or borrowed one from a library. But I bet more than a few of them bought the book in one form or another.

Did they all recommend the book to someone else? Based on this chart, no. But nearly half of them did (and, who knows, this chart could be incomplete).

But what I would be willing to bet money on is that, having loved the first book in the series, ALL of these folks were rabidly waiting for the follow-up volume, The Wise Man’s Fear. I bet most of them bought the book as soon at they could. I also bet they then continued to spread the word about this series of books they loved.

Just think about this for a second: the POWER that word-of-mouth has in book buying decisions. When I finish my novel, if I could get everyone who loved the book to tell just two friend who they think might like it, how many copies do you think that could sell? And if those two friends told two more friends, and they told two more, etc. etc., and if even just half of all these people told two friends, how many copies do you think that would sell? One person’s recommendation here set off nearly 30 people reading and/or buying the book, and probably close to all 30 buying the second volume of the trilogy. Think about that–think about the sales! It’s no wonder that Pat Rothfuss (besides being a great writer) made it to the New York Times bestseller list. This is the way The DaVinci Code, or Twilight, or Fifty Shades of Grey take off. Any meme that can propagate that fast is bound to make a mark.

So if you’ve ever doubted that the best way to sell books is word of mouth stop doubting…and start figuring out a way to generate that kind of word-of-mouth buzz for your book!

– S.