I'm rather fond of the story of the Pulitzer prizewinning poet Wallace Stevens, who worked as an insurance attorney by day, and did his writing during his free time. He considered his unexciting day job to be something that enabled him to do his writing, by giving his life a stable foundation that left plenty of mental resources remaining for doing what he loved.
Some choice quotes on the subject:
"It is necessary to any originality to have the courage to be an amateur."
"It gives a man character as a poet to have a daily contact with a job. I doubt whether I've lost a thing by leading an exceedingly regular and disciplined life."
Derek Sivers had a blog entry with similar advice. Have a tolerable day job so that your hobby can remain an enjoyable pursuit rather than trying to make your passion into a viable business.
I've heard it said that Kafka never wanted his works published and, during his lifetime, they weren't. But I agree with the general sentiment. Gene Simmons had pretty good advice about it: "Even Clark Kent had a day job".
Some choice quotes on the subject:
"It is necessary to any originality to have the courage to be an amateur."
"It gives a man character as a poet to have a daily contact with a job. I doubt whether I've lost a thing by leading an exceedingly regular and disciplined life."