The prejudice against the ill-regulated mind

From The Art of Thinking; or The Port-Royal Logic by by Antoine Arnauld and Pierre Nicole.

There is nothing more desirable than good sense and justness of mind, in discriminating between truth and falsehood. All other qualities of mind are of limited use; but exactness of judgment, is of general utility in every part, and in all the employments of life. It is not alone in the sciences, that it is difficult to distinguish truth from error, but also in the greater part of those subjects which men discuss in their every-day affairs. There are, in relation to almost everything, different routes the one true, the other false and it is reason which must choose between them. Those who choose well, are those who have minds well-regulated; those who choose ill, are those who have minds ill-regulated; and this is the first and most important difference which we find between the qualities of men's minds.

Indeed. One of the most subtle of prejudices but perhaps among the strongest. The prejudice against the ill-regulated mind which leads the unfortunate to foolish errors. The enemy of progress is the poorly populated mind that is also an ill regulated mind. See Congress.