Definitely agree with skydragon - "there are hurdles every step of the way that you don't see" EVERY author, even ones who appear to have made it, will have had some downs and some challenges, even if they don't talk about them. Whenever I do get chatting with authors I regard as doing well, I usually find there's something that's been difficult for them.
To share my experieneces: I queried my first manuscript when I was 10 (!) and it actually got some really nice personalised rejections (probably because I was 10...) I also queried two other fantasy MSs while I was at sixth form/university - I actually got a full request on one, with some really good feedback, but IIRC I lost interest in the book and moved on. I'd already edited and changed a lot and couldn't face doing more.
To move on from juvenalia:
MS #1 - YA crime thriller, maybe queried about 10-15 agents, got agent representation, sold to a Big 5 publisher. Was really pretty successful.
MS #2 and MS #3- also YA crime thrillers, contracted to Big 5 publisher... didn't sell well.
MS#4 - YA crime thriller, started writing, abandoned at a mature stage because I was starting to feel trapped writing similar kinds of books to my debut and wanted to do something different (probably not a great decision, looking back on it?!)
MS #5 - more of a psychological YA contemporary, subbed to 6-7 editors, didn't get great feedback, and I didn't love the story enough to want to gut-edit it for another round.
MS #6 - YA hitorical romance. MAN, I was so attached to this one. It was written slowly, under difficult circumstances, but my agent didn't like it. I rewrote it from the ground up based on her feedback, but she didn't like the second version either... so it got trunked.
MS #7 - YA dark contemporary. Agent didn't like it enough to sub. Left agent, queried about 15 agents, no one interested. Sent a revised version to my original agent. She had some reservations, but subbed it to two editors who passed. Agent wasn't happy submitting it further.
MS #8 - YA thriller. This was my "last chance saloon" book before moving on from YA. Luckily, I got a new agent more or less instantly. It came out in April. I'll always wonder how big a part me signing to write two IP books with the publisher played in them taking this book on - I'm guessing it made me as an author an easier sell.
I'm convinced that so much of publishing is luck - you can have a great book, but if it doesn't strike the right editor at the right publisher at the right time, it's going to be very hard. It's really difficult. I think we all know the feeling of getting excited about a new project while also simultaneously thinking "is this one going to go anywhere?"
Kate Dylan's sub stories is GREAT.