The Pharisee's prayer manifests his mindset (II Peter 2:3). People like him trust in their own works to gain salvation and eternal life, not trusting in Jesus Christ for them. They do not really think they need His sacrifice or help because they think they are good enough in themselves. So, they toot their own horns, making sure God knows how righteous they are. While kneeling before Him, they tell Him all the good things they are always doing, and believe that He is impressed. They act as if God owes them salvation because of their good works.
This attitude shows how little they understand of the true holiness of God and the lowliness of our spiritual state. While on earth, Jesus worked more easily with tax collectors and sinners than with the Pharisees, though the latter were more dedicated to adhering strictly to the letter of the law. The Pharisees, knowing they were more righteous, made sure others knew it. In their self-delusion and self-righteousness, they could learn little from Christ.
The Pharisee, considering others as nothing, treats them accordingly. It is typical of human nature to elevate itself while putting down others, and some believe that this is the only way to elevate themselves above their peers. Isaiah writes about such people: ". . . who say, 'Keep to yourself, do not come near me, for I am holier than you!' These are smoke in [God's] nostrils, a fire that burns all the day" (Isaiah 65:5).
The Pharisee compares his own flaws, not with God's infinite perfections, but with the imagined greater flaws of others. His pride has made him bankrupt of genuine compassion and concern (James 2:13). He presumptuously errs in his prayer in that it is neither his duty nor his right as a sinner to point out another's sins. In trusting in Christ for righteousness, our inadequacies and guilt are revealed, and we become willing to admit that others may be much better than we are.