From a 1986 interview to Leonard Michaels for Paris Review, seen in Jacket Copy:

It's a question of attention span, or maybe toilet training, for those novelists. Maybe they assume that a character is, like themselves, capable of astounding concentration on a subject, unrelieved for years and years. […] I've never met anyone, except for people who are profoundly depressed or trapped in some neurosis, who exhibited a novelistic consistency. Usually they can't remember where they were or what they did last week.