Even those who are chosen to teach others, and who should have no other purpose than to prepare themselves to teach those committed to their care, usually become subject to error as soon as they enter public life either because, having little time to themselves, they are incapable of concentration and of applying themselves to things that demand very much of them, or because, greatly desiring to appear learned, they boldly pronounce on all matters without reservation, and hardly suffer anyone to resist them or instruct them.