Two years later, he quit his job as a mailroom clerk in the Warner Brothers offices in Manhattan to write radio and television scripts with his brother Danny Simon, including tutelage by radio humourist Goodman Ace when Ace ran a short-lived writing workshop for CBS. They wrote for the radio series The Robert Q. Lewis Show, which led to other writing jobs. Max Liebman hired the duo for his popular television comedy series Your Show of Shows, for which he earned two Emmy Award nominations. He later wrote scripts for The Phil Silvers Show; the episodes were broadcast during 1958 and 1959.  Simon credits these two latter writing jobs for their importance to his career, stating that "between the two of them, I spent five years and learned more about what I was eventually going to do than in any other previous experience." He adds, "I knew when I walked into Your Show of Shows, that this was the most talented group of writers that up until that time had ever been assembled together." Simon describes a typical writing session with the show:  There were about seven writers, plus Sid, Carl Reiner, and Howie Morris...Mel Brooks and maybe Woody Allen would write one of the other sketches ... everyone would pitch in and rewrite, so we all had a part of it ... It was probably the most enjoyable time I ever had in writing with other people.  Simon incorporated some of their experiences into his play Laughter on the 23rd Floor (1993). A 2001 TV adaptation of the play won him two Emmy Award nominations. The first Broadway show Simon wrote was Catch a Star! (1955), collaborating on sketches with his brother, Danny.

Answer this question "Why did he quit?" by extracting the answer from the text above.
I spent five years and learned more about what I was eventually going to do than in any other previous experience.