People confuse the two audiences required for a perennial bestseller—or, really, any successful publication, regardless of your definition of success. This confusion makes the platform discussion more difficult. Let's clear it up.
First audience: the people who want to buy your book on a certain topic before you've even written it. As soon as the people in the first audience find out that X has written a book on Y, they're sold.
"Music producer Rick Rubin wrote a book on creativity? Where can I get it?"
As a member of Rubin's first audience, I learned that the book is coming out in January and pre-ordered it. (Well, snagged a galley.)
Second audience: the people who might be persuaded to buy a book on Y based on the opinions of those in the first audience.
"Dude! You have to read Rick Rubin's new book. It's great."
"Who is this? Where did you get this number? Why are you breathing so heavily?"
The first audience won't necessarily buy anything you write. If they know you for Y, they'll buy a book from you on Y. Not Z.
Likewise, the second audience could be persuaded to buy a book, but not on anything. On Y. If someone they trust tells them you've written a really great book on Y, they'll buy it.
If you write a newsletter about dog training and announce that you've written a book about dogs, many of your newsletter subscribers are likely to buy it. If they think it's good, they'll recommend it to others. Their friends with dogs may act on that recommendation.
On the other hand, if you announce a book about organic farming, very few of your newsletter subscribers will buy it. This is true even if you have lots and lots of newsletter subscribers. They read your newsletter, sure, but they don't read it for organic farming advice. Even if they farm themselves—unlikely—they have no reason to consider you a farming expert.
Also, even if your subscribers buy the farming book out of sheer loyalty, and even if they recommend it to others, the people they know are far less likely to be appropriate targets. Less likely to be farmers, and less likely to trust the recommendation of dog-lover friends who are inexplicably recommending farming books.
Gosh, this seems obvious as I'm writing it. Yet many first-time authors need to be told this.
One problem is, first-time authors think only of the second audience. They focus on creating a book that will be, essentially, easy to recommend. If someone heard about this book on a podcast, or it was recommended in a newsletter, would they want to buy it? Without a first audience, a second is far less likely to discover you, no matter how snappy your subtitle.
How do you build a first audience? This is a video of Bryan Cranston and Aaron Paul hawking tequila at a random Costco. I could have picked a fun, well-produced video of similar audience-building efforts, but this crowded aisle conveys the vibe better. Cranston and Paul are down in the trenches, selling. Ugh.
"But Dave, these are celebrities. They already have a first audience." Wrong. Do you associate Breaking Bad with tequila? If you told me Cranston and Paul were promoting a new brand of crystal meth, sure, I'd be first in line. Sign me up for that yummy blue crank. But not tequila.
We see the successful celebrity booze brands and forget that many, many more celebrities would love to shore up their residual income with a high-margin liquor brand. Where's Jason Alexander's Brandy Alexander? Where's Joe Piscopo's Pisco? These things don't sell themselves no matter how famous you are because you're not famous for liquor. Cranston and Paul knew they'd need to build their tequila's first audience by hand before they could expect any momentum with a second. If that meant convincing Costco shoppers to taste some, so be it.
When people say "publishers don't market books anymore," they confuse first audiences with second audiences. Publishers—traditional and hybrid—can help a book work...with a second audience. The same is true of publicists. However, if thousands of people (minimum) aren't already eager to buy your book—often because tens of thousands (minimum) already read your stuff on the same subject online—the earnest efforts of publishers and publicists will probably be in vain. Get yourself into orbit if you expect your publisher to get you to the Moon.
As you can see with Cranston and Paul, building a first audience is an ugly job. It's also usually invisible to the rest of us, so we assume the process somehow isn't ugly for others. We see the effort with this tequila brand because Cranston and Paul are celebrities. The fact that they're shilling in Costco is, in itself, noteworthy in the media. They're so down-to-earth and hardworking, they're friends in real life, etc.—good narrative. Thus, the rare opportunity to watch the sausage getting made.
When a would-be author sees someone they've never heard of take the TED stage or appear on a major podcast to promote a bestselling book, they believe that the book is a bestseller because of the TED talk or podcast appearance. Therefore, they believe that their first goal should be doing a TED talk or getting on a big podcast. However, that author is only on that stage or podcast because they did the hard, ego-busting work of building a first audience to justify the opportunity to appear in front of a second.
One last point: first and second audiences work in tandem. There are lots of TED talks. Lots of podcast episodes. Even people who often watch TED talks or subscribe to a given podcast are selective about which talks and which episodes. There's far too much content. So even if you elbow your way onto a big stage, real or virtual, that appearance is far less likely to go viral without thousands of members of your own first audience spreading it around.
If you want a second audience, build your first. Don't hire someone to do it, either. A first audience is something you have to build yourself. Hire a web designer or an audio engineer, sure, but ultimately you'll be the one walking the aisles of Costco with a tray full of samples. It's an ugly job, but only you can do it.