King said it started when Kirby McCauley asked him to contribute an original tale to his 1980 "Dark Forces" anthology.
"I said: 'Kirby, I don't think I can do that because I'm blocked. I'm not writing anything," King recalled in New York while promoting the film version of "The Mist."
"I had finished three books," King said, referring to "Carrie," "Salem's Lot" and "Night Shift."
"And I was kind of stuck, really, and I happened to be in the local market one time and a lot of people were shopping, little town market, and I looked at the front windows and I thought, 'You know, if something bad happened, those windows would all blow in.' Because that's the way I think. It's not necessarily a good thing, but it's been a profitable thing over the years."
King said his story about townspeople trapped in a grocery store, fighting for their lives, then unfolded "very, very naturally."
"I've always been grateful to 'The Mist' because it kind of broke me out of a place where I couldn't seem to do anything."