Hawzah News Agency – Imam al-Sadiq peace be upon him says:   

أنفَعُ الأشياءِ لِلمَرءِ سَبقُهُ النّاسَ إلى‏ عَيبِ نَفسِهِ.

‘The most beneficial thing for a man is his precedence over others at knowing his own fault.’

Source: al-Kafi, v. 8, p. 243, no. 337