In one of the letters, Screwtape expresses concern that Wormwood's "patient" has begun to develop humility. He is no longer self-confident. He is no longer making "lavish promises of perpetual virtue." He is simply hoping in daily, hourly grace.
"This is very bad," says Screwtape. Then he gives this bit of instruction:
"I see only one thing to do at the moment. Your patient has become humble; have you drawn attention to the fact? All virtues are less formidable to us once the man is aware that he has them, but this is specially true of humility. Catch him at the moment when he is really poor in spirit, and smuggle into his mind the gratifying reflection, 'By jove! I'm being humble,' and almost immediately pride--pride at his own humility--will appear. If he awakes to the danger and tries to smother this new form of pride, make him proud of his attempt--and so on, through as many stages as you please."
How many of us have fallen into this devilish trap! When we think we're actually starting to be humble, we gloat over it. This makes humility the most elusive virtue. We all know we should be humble, but as soon as we think we've got it, we've lost it. The only genuinely humble people don't realize it, because genuine humility is never self-conscious.
How, then, can we develop this virtue? I think it only comes when we consciously direct our attention to the Lord Himself. As John Piper writes,
"Is not the most effective way of bridling my delight in being made much of, to focus on making much of God? Self-denial and crucifixion of the flesh are essential, but O how easy it is to be made much of even for my self-denial! How shall this insidious motive of pleasure in being made much of be broken except through bending all my faculties to delight in the pleasure of making much of God!"
Have you bent all your faculties to delight in making much of God? Only when our boast is in Christ and His cross and nothing else will we become genuinely, unconsciously humble.
 C. S. Lewis, The Screwtape Letters (San Francisco, CA: HarperCollins, 2001) 69. John Piper, The Purifying Power of Living by Faith in Future Grace (Sisters, OR: Multnomah Books, 1995) 97.