Quintillian, Institutio Oratoria 3.6:
“I now confess that I find myself of a slightly different opinion than that which I once entertained. Perhaps it was safest for me, in my pursuit of fame, to change nothing of that which I not only thought but even approved for many years. But I do not feel that I was conscious of my judgment having been deluded in any part, especially in that work which I composed with an eye to some use by noble youths. Even Hippocrates, famous for his medicinal art, seems to have acted most nobly in confessing certain of his own mistakes, lest posterity be led astray by them. Even Cicero did not hesitate to condemn some of his previously published works with new books, such as his Catulus and Lucullus and those, of which I have just spoken, about the art of rhetoric.
Indeed, all extended in study would be an entire waste of time if one could not expect to find something better than what has already been said. Yet, none of those things which I formerly taught was an idle waste of time; even the things which I will now teach will be returned to those same particles.
So, let it never be a source of regret for someone to have learned from me: I will just try to collect and outline those things in a more significant way. I hope that it is clear to all that I am not making this discovery plain to others later than I persuaded myself of it.”
Ipse me paulum in alia quam prius habuerim opinione nunc esse confiteor. Et fortasse tutissimum erat famae modo studenti nihil ex eo mutare quod multis annis non sensissem modo verum etiam adprobassem. Sed non sustineo esse conscius mihi dissimulati, in eo praesertim opere quod ad bonorum iuvenum aliquam utilitatem componimus, in ulla parte iudicii meI. Nam et Hippocrates clarus arte medicinae videtur honestissime fecisse quod quosdam errores suos, ne posteri errarent, confessus est, et M. Tullius non dubitavit aliquos iam editos libros aliis postea scriptis ipse damnare, sicut Catulum atque Lucullum et hos ipsos de quibus modo sum locutus, artis rhetoricae. Etenim supervacuus foret in studiis longior labor si nihil liceret melius invenire praeteritis. Neque tamen quicquam ex iis quae tum praecepi supervacuum fuit; ad easdem enim particulas haec quoque quae nunc praecipiam revertentur. Ita neminem didicisse paeniteat: colligere tantum eadem ac disponere paulo significantius conor. Omnibus autem satis factum volo non me hoc serius demonstrare aliis quam mihi ipse persuaserim.