From a classic on the interior life:
The fund of pride there is in us.
Pride is the love and desire of our own superiority. It is of all our vices the most hidden, the most deeply rooted, and that of which the occasions are the most frequent. These are occurring every hour; either with respect to the goods and advantages which we possess and from which we draw matter for self-complacency, exaltation of ourselves above others, and desire to be esteemed and praised, or with respect to the evil and the faults that are in us, and which we try to conceal, to disguise, to diminish, to excuse, and are unwilling even to inwardly acknowledge. In one day we are guilty of more than one hundred acts of pride…
To become like God we must renounce all resemblance to the devil, which consists in pride, vanity and presumption; as also all resemblance to brutes, which consists in the passions and the disorderly movements of the sensual appetite.
Every vice produces in the soul four evil effects: 1, it clouds and blinds it; 2, it defiles it; 3, it disquiets and harasses it; 4, it enfeebles it. But of all vices, that which specially darkens the mind is pride; and that which specially defiles the heart is pleasure.
We are naturally always disposed to let ourselves be captivated by the splendor of honors and the applause and esteem of men, and by the allurements of pleasure and gratification of our senses, because we suffer grace to have but very slight dominion over our mind. For the same reason, if any one says a word about our faults, we cannot endure it. It will excite in our heart fifty movements of anger, vexation, bitterness and impatience.
Strange injustice of the human heart! God has forgiven us sins innumerable; and yet we cannot forget a disobliging word which has been said to us, or a slight affront which has been offered us; we continue to preserve the remembrance of it, and wait only for an opportunity to testify our displeasure. This comes of the foolish esteem and false love which we entertain for ourselves. We think more of our own interests than those of God; pride blinds us.
The malice of our proud heart is manifested also in this, that if any one has the least defect, although he may excel in everything else, we pass over all the perfections he possesses and fasten upon the one defect; we think of it, we talk of it, we take occasion thereupon to reckon such person our inferior and inwardly to exalt ourselves above him; so that, in fact, we rank in our own estimation above everybody in the world.