Your success in publishing will ultimately come down to this question. Of course there is a degree of talent, luck, and timing thrown in, but once those come together it will become about how bad you want it. The first hardship is wading through the rejections. Many writers with a great story give up because this part of the process can be so discouraging. See my previous entry on turning rejection into motivation. You can get through this part, don't despair!
Once you've been picked up there is a mountain of work ahead of you and you'll need a lot of motivation to climb it. First will be the round (s) of edits your agent recommends. At times they'll be brutal so you will need the skin of a rhino. Just remember they are ultimately for the good of your novel and your agent has the work's success in mind. Next get ready for rejection all over again. When it's ready your agent will begin submitting it to editors and the rejection letters could very well begin again. Don't fret though, your agent will likely approach several editors over the course of a year and just because the first few say no doesn't mean they all will. Editors are like agents after all and they really have to be excited about your work to be willing to pick it up. If you're really lucky your book could go into auction, meaning several editors are interested and a bidding war will ensue. This is definitely cause to celebrate if it happens.
When that magical moment finally arrives and a publisher offers you an advance, the work is still not over. From here there will be several rounds of editing (yes, more editing) and this time there will be deadlines. Expectations are high, and rightly so because they've invested money into you. Finally, when all of that is finished, you're still not done. You can't expect the publishers to do all the promoting for you. Some do very little, some do a lot. This often depends a lot on the size of the advance. The more they invest in you, the more they have at stake.
Be prepared to do some of your own promoting, and it never hurts to start ahead of time. Start building your platform from the moment you finish your novel. Blog, Twitter, join an online writers group or website. An established platform will look very attractive to both agents and editors. Platform=readers, it's that simple. Also, be prepared to set up your website for your book once it's been picked up by a publisher. They may not offer you a site, or might just give you a mention on theirs. It will help bring readers to you and keep the one's you have if you plan on having a good site.
Now that mountain is starting to look like Everest isn't it? This is why you can have a phenomenal book but still fail if you don't want it really bad. But now you are forearmed, knowing is half the battle!
Discouraged? Check out this success story from an author who self published first: http://www.crunchgear.com/2009/07/11/indie-kindle-author-lands-book-deal/