I suspect what happened here (and possibly in other similar cases) is that some author glossed a body of work in a way that made sense in context, and others mistook it as a quotation. It's as if I remarked that Isaac Asimov said a lot of prescient things about robots, and people saw that and started quoting it:
To be ignorant of what occurred before you were born is to remain always a child. For what is the worth of human life, unless it is woven into the life of our ancestors by the records of history?
