I've seen the if only we get (tiny percentage) of (huge number) to pay (seemingly small amount), we'll be rich! arguement framed about a thousand different ways. I actually cautioned an entrepreneur I was talking to last night about this.

Sales start from 0, and they continue from there. Until you have sold it a few times, who knows if .1% is incredibly easy or impossible. Sometimes any number >0 just isn't going to happen.