Some time ago I received a submission that went something like this (names and details have been changed to protect the innocent, guilty, and all those in between):

I’ve published three successful nonfiction books. All three, in the area of business and leadership, are still selling very well. One of them, coauthored with Bill Gates (with a foreword by Warren Buffett), reached bestseller status and has sold more than 1 million copies to date.  My weekly email newsletter, Lead On!, reaches more than 20,000 influential and rising business leaders and government officials. Also, while promoting that book with Mr. Gates, I appeared on Fox and Friends and CBS This Morning, as well as numerous other radio and television talk shows. I am also featured in an interview in Forbes magazine, which is scheduled for next July.

I’m pleased to present to you my proposal for a 90,000-word fantasy novel, the first of a trilogy set in an alternate universe. The story eerily reflects some of the current events we’re facing in our world today.

Notice anything amiss?

Agents and editors encounter this sort of thing more often than you might imagine. A writer who has enjoyed good success and built a strong platform in one arena wants to spread his or her wings and fly … off into a substantially different neighborhood (much like my mixing of metaphors, you might say).

But can you see the problem? It’s the disconnect between the two paragraphs above. All of the wonderful and persuasive platform details mentioned in the first paragraph come tumbling down when the agent or editor reaches the second paragraph. The kind of platform that might recommend a business writer to an agency or publishing house is not transferable to what a writer of fantasy fiction would need. You could pretty much throw out all of that writer’s past reach and exposure and say, “Let’s start from scratch in building a completely new platform.”

Sure, you can probably think of an exception: a famous romance author whose book of recipes became a bestseller or the politician who also writes children’s books. But the exception proves the rule. And famous people live by different rules. (So, if you’re famous, give me a call.) For most of us, however, it takes a good long while to build a platform that is strong enough to seem persuasive to agents and editors. If you’ve managed to do that, be very cautious about expanding into new territory that will make your existing platform useless.