As the country's most resoundingly unpublished writer, I can testify that it's a lot easier to write a "best seller" than it is to find a publisher who agrees with your assessment

Ayn Rand's "The Fountainhead" was rejected by 12 pubs. But with the advent of the word processor, I estimate it's 25 times easier to write a book; and using the Internet it's 25 times as easy to address a potential market. Given those figures, a typical publisher probably gets 625 times the input load. To find one that liked her book enough to publish it, might today require 12 x 625 = 750 queries

If the book occupied, say, 200 written pages and typing at the time cost, say, $2 a page, then you had to submit a $400 MS to one pub at a time, with return postage

Even today, in order to discourage overloading of its hard drives, a pub showing any interest might ask for a printed copy. You will be very lucky if your 750 queries result in 75 such requests

Postage notwithstanding, that's 75 x 20 = 150,000 pages

Don't write a book

dalehileman