You know, Donald Barthelme once told me, in one of his books (Not Knowing,) that you can't fucking plan it.
That's fine, but then how do you get a line like "Many years later, standing in front of the firing squad, Colonel Aureliano Buendia recalled the day his father took him to discover ice," or however opens.
Not that a huge amount of that book wasn't improvised, or however you might describe unplanned writing. But Marquez himself has said he planned that thing thoroughly. So? Not knowing.