So, the guys starting the company were excited, because they said "We know the odds are small, but we don't need much, if just 1 in 1000 buys our product we're rich, as that's like 350K people in the US. And how difficult would be to get 1 in 1000 to buy our stuff with a little marketing? It's a great product anyway! Heck, if just 1 in 10,000 buys our product, that's still 35K sales, enough to bootstrap the company and make some decent profit! And 1 in 10,000 should be trivial!"
Ultimately, though the message the author of the post got from that business plan failing miserably, is that there's always the posibility of 0 in 1000 buying their product...
"Just get 1000 true fans" downplays the difficulty.