One of the best commentaries (and a true classic) on the book of Proverbs is the one by Charles Bridges.
You can download it for free here .
Here are his excellent comments on Proverbs 18:12 – Before his downfall a man’s heart is proud, but humility comes before honor.
We have had both of these proverbs separately (16:18; 15:33). Surely this repetition was intended to deepen our sense of their importance. It is hard to persuade a man that he is proud. Everyone protests against this sin.
Yet who does not cherish the viper in his own heart?