I hope you're not expecting your book to support you financially. That's pretty rare, especially when self-published.
For me the hardest part is marketing. The types of people who go into writing are kinda the opposite of those who go into marketing. I hate that being a writer means you have to do/know everything about publishing, have an existing fan base or professional reach, etc - even when you have a publisher!
It's a tough life, but all worth it when you see someone's face light up as they say, "Oh, you wrote a book!?"