It is a good thing to recognize one’s own faults.

[Bellum est enim sua vitia nosse.]

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

Epistulae ad Atticum [Letters to Atticus], Book 2, Letter 17, sec. 2 (2.17.2) (59 BC) [tr. Winstedt (1912)]
    (Source)

Speaking of his own slight "vanity and thirst for fame."

(Source (Latin)). Alternate translation:

It is well to know one's faults.
[tr. Shuckburgh (1900)]

It is a great thing to know our own vices.
[ed. Harbottle (1906)]

It is a fine thing to recognize one's faults.
[tr. McKinlay (1926), # 14]

It's a fine thing to know one's failings.
[tr. Shackleton Bailey (1968), # 37]