It is certainly not the least charm of a theory that it is refutable; it is precisely thereby that it attracts the more subtle minds. It seems that the hundred-times-refuted theory of the "free will" owes its persistence to this charm alone; some one is always appearing who feels himself strong enough to refute it.
But the most brilliant propagandist technique will yield no success unless one fundamental principle is borne in mind constantly and with unflagging attention. It must confine itself to a few points and repeat them over and over. Here, as so often in this world, persistence is the first and most important requirement for success.