His usual routine was to awake at 6 A.M., sit down at the typewriter by 7:30 and work until 10 P.M.
In "In Memory Yet Green," the first volume of his autobiography, published in 1979, he explained how he became a compulsive writer. His Russian-born father owned a succession of candy stores in Brooklyn that were open from 6 A.M. to 1 A.M. seven days a week. Young Isaac got up at 6 o'clock every morning to deliver papers and rushed home from school to help out in the store every afternoon. If he was even a few minutes late, his father yelled at him for being a folyack, Yiddish for sluggard. Even more than 50 years later, he wrote: "It is a point of pride with me that though I have an alarm clock, I never set it, but get up at 6 A.M. anyway. I am still showing my father I'm not a folyack."
The New York Times, April 7, 1992