Like many emerging writers, I thought the mere act of writing a book would bring me cash flow and semi-fame. I figured most people never finish writing theirs, and those that did would probably never submit. I'd have it made by finishing mine, giving a good, clean edit and sending it off to the magic world of agents. They'd read the first couple of pages and go, "WOW!" and contact me immediately with a big contract. Sheesh. How wrong was I?
Writing a book is hard, but there are loads of people out there with not only one, but multiple manuscripts waiting for representation. Finding an agent is one of the most difficult things one can do on this earth, but I've heard being on submission is even worse. And money, if any, isn't going to start pouring in. It may trickle, it may spurt, but it isn't going to be like an avalanche of green. The publishing industry is in a weird state presently, and money is following along in cautious step.
And patience. I wrote my first manuscript in a month, but it took years to shape it into something I could be truly proud of, then another year of working with an editor. It takes months to hear back from agents, it takes time to be on submission; if you're a short story writer it takes many months to hear back from journals, and even longer to see your work in print. Any writer who believes they can bypass all this waiting will only find themselves on the losing end. Remember what happened in the Tortoise and the Hare?
And it's no different for those who self-publish. I've witnessed the process and can say that while a SP book generally has a faster release date than that of someone who has followed a more traditional route, there is still much waiting to be had, and a lot more pressure to promote. Bookstores and libraries are often less willing to stock a self-published work.
So, go into writing with realistic expectations. Instead of placing your enjoyment on the idea of money and instant fame, put it where it really belongs: the actual writing, the joy of your character's actions, the satisfaction of a job well done. That, in the end, is what matters.