Every once in a while, I'll read about indie authors considering quitting because their books aren't selling. In some cases, I think it's just a case of unrealistic expectations. IMHO, any author who has just published a first novel and wonders why it hasn't sold a thousand copies in the first week is delusional. On the other hand, there are also authors with multiple books that have been available for years, and their books still aren't selling. Should they quit? That's a tougher question.
I know how they feel because I've entertained the same thoughts recently. My publishing career is still relatively young (about two years), but I now have three novels and two short story collections for sale. I thought that I had somewhat realistic expectations going in, but sales still aren't up to my modest goals or compared to what other indie authors are seeing. Fortunately, I have a full time job and don't need to rely on book sales as my primary source of income. However, my sales results still make me wonder sometimes if I should give up.
Whenever I think about it, however, my answer is no. The simple reason is: I've been writing all of my life, so even if I "quit", what does that mean? I don't see myself not writing anymore. It's just not going to happen. So does quitting mean that I won't publish what I write? Perhaps, but given the ease with which authors can self-publish their books nowadays, I don't see a reason why I wouldn't want to publish a story that I believe is good and that people will want to read. It would be another situation altogether if readers gave my books bad reviews and told me that my writing sucks. Then I would feel bad about putting books out there for public consumption, much less making people pay for them. But the few reviews I've gotten so far have been positive for the most part. My problem doesn't seem to be that I'm writing crap, just that people aren't finding what I write. To me, that isn't a good enough reason to quit. I don't know if enough readers will ever find my books, but it shouldn't stop me from writing them.
For other authors out there who are thinking of quitting, I think the decision boils down to why you started this business in the first place. Is it to make a lot of money? Is it because you have an urge to write? Some other reason? For me, unless I don't want to write anymore, quitting isn't even an option.