For many, many years the world of publishing was set in its ways and it was difficult for new authors to get that fabled publishing contract. The traditional route was for someone to toil away at writing if not all, then most of, their manuscript. This was then used to tease agents into acting for the aspiring author, or perhaps an outline was sent round the publishing houses to tempt a buying editor to sit up and take notice.
So many things could go wrong; your historical romance lands in someone's lap who already has "their" historical writers in place, maybe your cross-over zombie/vampire western is allocated to a reader who hates the un-dead, loathes blood-suckers with a vengeance and the last Western they liked was John Wayne's The Searchers or maybe the professional reader is just not in the mood for that particular type of thriller.
Perhaps the book is hard to pigeon-hole into a specific genre?
Who knows what the issues might be; the fact is that the publishing world abounds with urban legends of now-famous authors who faced rejection after rejection, before someone spotted their genius, or their marketability, and they were off.
Then there is the time it takes to fine-tune and develop a book - and all this is in someone else's timeline; someone is in control - but it isn't you.
And then there was revolution - an e-revolution.
Amazon opened up its Kindle e-book store to self-publishers through its Kindle Direct Publishing ("KDP") platform and the writing world would never be the same again.