Raymond Carver, who worked many jobs (including as a janitor, and a textbook editor), writes:

I have friends who’ve told me they had to hurry a book because they needed the money, their editor or their wife was leaning on them or leaving them – something, some apology for the writing not being very good. ”It would have been better if I’d taken the time.” I was dumbfounded when I heard a novelist friend say this. I still am, if I think about it, which I don’t. It’s none of my business. But if the writing can’t be made as good as it is within us to make it, then why do it? In the end it’s all we have, the only thing we can take into the grave. I wanted to say to my friend, for heaven’s sake go do something else. There have to be easier and maybe more honest ways to try and earn a living. Or else just do it to the best of your abilities, your talents, and then don’t justify or make excuses. Don’t complain, don’t explain.

I first came across this passage through Haruki Murakami quoting it in Novelist as a Vocation, where he adds:

Since I put everything into their creation, I will never have to say, “It would have been better if I’d taken the time.” Whatever limitations they have are the result of my own deficiencies at the stage I wrote them, nothing more. That’s too bad, but nothing for me to be ashamed of. Deficiencies can be overcome if you work hard enough. A missed opportunity, however, can never be regained.