We may go to God in prayer and have a higher opinion of ourselves than God has of us. Is that possible? Looking at the holy man praying in Jesus' parable we see that in his prayer he truly believes that he is righteous compared with the dishonest tax collector.
So we would expect the holy man praying to be better than the tax collector as he stands before God and yet Jesus says that the holy man is in need of humility in prayer. The tax collector has it. He prays, "God, be merciful to me, a sinner!" Jesus says pray with humility. saying, "Our Father, ...Forgive us our tresspasses as we forgive those who trespass against us."
The expression 'Eating Humble Pie' means that others see the wrong we have done and call us out on that wrong. We've been caught in a lie, a sin, a disgrace, or have some something very dishonest and been seen. God sees us as we truly are.
God our Heavenly Father knows all of our hearts-- our secrets, sins, and wrongs. When we pray to God we ask for forgiveness in Jesus Name, eating humble pie, and God forgives us. Always.
He also told this parable to some who trusted in themselves that they were righteous and regarded others with contempt: “Two men went up to the temple to pray, one a Pharisee and the other a tax collector. The Pharisee, standing by himself, was praying thus, ‘God, I thank you that I am not like other people: thieves, rogues, adulterers, or even like this tax collector. I fast twice a week; I give a tenth of all my income.’ But the tax collector, standing far off, would not even look up to heaven, but was beating his breast and saying, ‘God, be merciful to me, a sinner!’ I tell you, this man went down to his home justified rather than the other; for all who exalt themselves will be humbled, but all who humble themselves will be exalted.” Luke 18:9-14