I buy dog food in a fifty-five pound bag. Every day I feed my dog one cup of the pellets. It seems impossible but little by little I empty that huge bag and have to buy another.
Writing a novel is like emptying that dog bag (in reverse I admit). One cup (four pages a day) seems an unlikely amount to make a dent in anything, but the constant, everyday accumulation of those words become 28 pages a week, 120 pages a month, and in six months you have a first draft and you have to buy a new bag of dog food.
Writers write a lot.