According to Garrison Keillor's Writer's Almanac yesterday:
It was on this day in 1920 that This Side of Paradise was published, launching 23-year-old F. Scott Fitzgerald to fame and fortune. The first version of the book was called The Romantic Egotist, and Fitzgerald had started writing it in the fall of 1917 while awaiting commission as an army officer. He wrote most of the manuscript at Fort Leavenworth, Kansas, and sent chapters as he wrote them to a typist at Princeton where he had been a student. In March 1918, he submitted the novel to Charles Scribner's Sons. Scribners rejected the novel but encouraged Fitzgerald to revise it. He submitted a new version titled The Education of a Personage to Scribners in September 1918, but that second version was also rejected.
In July 1919, after his discharge from the army, Fitzgerald returned to his family's home at 599 Summit Avenue in St. Paul. He pinned revision notes to his curtains and rewrote much of the novel. In August 1919, Fitzgerald finished a new draft, now titled This Side of Paradise. He gave it to a friend from St. Paul for a final edit and sent the new typescript to Scribners on September 4, 1919. Two weeks after he mailed the manuscript, Fitzgerald received Maxwell Perkins' letter accepting the book. Fitzgerald was so excited that he ran outside and stopped cars on the street to announce the news.