We've all read the "rock star" successes, the “I published a book and now I'm paying all my bills and taking trips to Europe!” And very little of the failures, lets face it no one wants to spend time writing about how they've not made anything and its so frustrating and they are quitting...they just quit.
Likely you, like me, will fall in with the majority, somewhere in that gray middle ground.
I haven't (yet!) gotten a best seller, though I've hit about 40,000 on Amazon's sales ranks and I'm happy with that, especially with the 500,000+ titles out. I started my business in late January and its only late March, I think those are decent numbers. But I have also submitted pieces that have only sold 1 copy. Granted that's $2 bucks in my pocket, but every book you put out you secretly hope the world loves as much as you do.
Yesterday I got paid for January's sales - they weren't huge, only enough to take my family of three to a cheap dinner, but next month I'll get the opportunity to pay a bill or two with it, and in two months it looks like it will have grown again.
The idea that "if you write it they will come" has been expressed multiple times out there, but realize they may or they may not. Don't quit your day job until you have a good chunk of change in the bank to support your writing career, because the truth is that your story will be your own, and no one else will have it.