Of any man at all it is to err, to persist in error is of none except unthinking; for the later thoughts, as they say, are usually the wiser.
Cuiusvis hominis est errare, nullius nisi insipientis in errore perseverare; posteriores enim cogitationes, ut aiunt, sapientiores solent esse.
Original text (Latin)
Notes from Wikiquote
Philippica XII, 5; translation of Walter C.A. Ker