For it is the characteristic of folly, to have eyes for the faults of others, and blindness for its own.

[Est enim proprium stultitiae aliorum vitia cernere, oblivisci suorum.]

Marcus Tullius Cicero (106-43 BC) Roman orator, statesman, philosopher

Tusculan Disputations [Tusculanae Disputationes], Book 3, ch. 30 (3.30) / sec. 73 (45 BC) [tr. Otis (1839)]
    (Source)

(Source (Latin)). Alternate translations:

For it is the property of Folly, to look upon other mens Failings, and to forget their own.
[tr. Wase (1643)]

For it is the peculiar characteristic of folly to discover the vices of others, forgetting its own.
[tr. Main (1824)]

For it is the peculiar characteristic of folly to perceive the vices of others, but to forget its own.
[tr. Yonge (1853)]

It is the peculiar quality of a fool to perceive the faults of others and to forget his own.
[Source (1882)]

It is the property of folly to see the faults of others, to forget its own.
[tr. Peabody (1886)]

This is just how foolish people behave: they observe the faults of others and forget their own.
[tr. Graver (2002)]

It is a trait of fools to perceive the faults of others but not their own.