One point, I think worth remembering is that writing a book and getting it published are two completely different things. Writing a good story, editing it, re-writing it, taking on board criticism, learning to be objective with your own script, being brutal, dealing with self-doubts, angst and general insecurities are all part of the journey (sorry I hate that phrase hijacked as it has been by the X Factor/Voice/add any talent/reality show - world).
Then, once you are eventually as happy as you can be with your work - you'll never be completely happy so don't expect that - it's time to learn how to get published - how to approach agents, write query letters, synopsis's, biographies, elevator pitches, what to add in, how many words to use, how to find out your genre (if it's not obvious). Finding agents/publishers that dabble in your genre, who might lower themselves to read your carefully crafted submission, is a huge undertaking in itself.
Then, of course, you have to take on and deal with the criticism (if you're lucky) or more likely, the complete indifference your submission produces and either change and re-submit or give up and start afresh on something else. (Or self-publish - another huge learning curve).
Personally, I always find the submission bit much harder than actually writing the book, because suddenly you are no longer master of your own destiny, sitting typing in your own world with no expectations and no competition. Now, you are in the dog eat dog world where everyone and their dog ( the one's that have not been eaten) are trying to get their book published and it is tough, perhaps it's designed that way to sort the wheat from the chaff, the men from the boys, the girls from the ladies and whatever the gender neutral equivalent may be.
Which is why you have to enjoy the creative process. If you enjoy making stuff up then chances are you'll cope, as the pay off of doing that, will make up for the hard work that lies ahead, and also if you enjoy it chances are, that will translate into the end product making the story better and easier to read.