Robert Shea, Robert Anton Wilson's writing partner for ILLUMINATUS!, began his literary career with a joke and accelerated it after losing his job.
The two worked as editors in Chicago for the Playboy magazine's "Playboy Forum" feature. The "Playboy Forum" received many letters containing conspiracy theories. Depending on which account you read, either Shea or Wilson suggested that it might be funny to write a novel based on the premise, "Suppose all these nuts are right, and every single conspiracy they complain about really exists."
Wilson left Playboy went on to make a career of writing books largely inspired by the success of ILLUMINATUS!, but according to Wilson's account in Chapter 4 of Cosmic Trigger Vol. 3, My Life After Death, Shea might never have written another book if he hadn't suddenly lost his job at Playboy. Wilson writes, "When Playboy fired him, Shea endured terrible anxiety about keeping his house, and dashed off a few novel outlines while looking for another job. He sold his first novel before finding a job and never stopped writing again." The Wikipedia entry on Shea lists seven published novels and two that were uncompleted or unpublished. Shea died of cancer in 1994 at age 61, cutting short an active literary career.
I tried to fact-check Wilson's account by writing to Mike Shea, the author's son, who maintains the official Robert Shea Web site, where electronic versions of all of Shea's books may be downloaded for free. After consulting his mother, Mike Shea wrote back, "Yep, your version is pretty much how it happened. According to my mom: 'He was writing at night and was looking forward to having the time to write all day, too!'."
I've only read Shea's Shaman, but I've just started All Things Are Lights.