Garcia Marquez wrote some of the most fantastical fiction of the century, yet he kept calling himself a journalist. That wasn't false modesty. The reporter's discipline, and one hard rule about credible detail, sat underneath everything he made up.

The Direct Answer
Treat fiction like reporting. One true detail makes the whole invention believable.
He laid this out in Peter Stone's 1981 Paris Review interview, The Art of Fiction No. 69.

Journalism Was His True Profession

Garcia Marquez never let go of his start as a reporter. He'd done the grind early, several stories a week plus daily editorial notes and film reviews, and he kept insisting the newsroom was his real home even after the Nobel. He saw fiction and journalism as close relatives rather than opposites, two ways of telling the truth that fed each other.

I've always been convinced that my true profession is that of a journalist.

Gabriel Garcia Marquez, Paris Review, 1981

The point wasn't nostalgia. Reporting taught him how to make a reader believe something, which turned out to be the exact skill a novelist needs most. When you're asking people to accept flying carpets and a rain of yellow flowers, the craft of making it land is everything, and he'd learned that craft on a deadline.

One True Thing Sells the Lie

His sharpest piece of advice came from comparing the two trades. In journalism, he said, a single false fact poisons the whole report and the reader stops trusting you. In fiction it runs the other way. One true detail can make an entire invented story believable. A precise, real-feeling fact in the middle of the impossible is what convinces the reader to go along with the rest.

That's why his magical scenes are so heavy with concrete, ordinary specifics. The number of something, the weather, a brand, a smell. He grounded the unreal in reporting-grade detail so the strangeness felt reported rather than dreamed. You can see the same instinct in how he set up his desk and his hours, covered in the full Gabriel Garcia Marquez writing routine.

Patience was the other half of it. He'd spend a whole morning on four or five lines and tear them up the next day if they weren't right. That's the opposite of how he'd worked on deadline, yet it came from the same value, getting it true before moving on. He carried the reporter's respect for accuracy into prose nobody could ever fact-check, and held himself to it anyway.

What You Can Steal