How does the Bible address an unhealthy self-confidence?

Luke 18:9Jesus told this story to some who had great confidence in their own righteousness and scorned everyone else

Philippians 3:3-4We who worship by the Spirit of God are the ones who are truly circumcised. We rely on what Christ Jesus has done for us. We put no confidence in human effort, though I could have confidence in my own effort if anyone could. Indeed, if others have reason for confidence in their own efforts, I have even more!

When self-confidence leads us to see ourselves as better than we are and better than others we are in danger of immediate or eternal disappointment.

1 Samuel 15:32Then Samuel said, “Bring King Agag to me.” Agag arrived full of hope, for he thought, “Surely the worst is over, and I have been spared!”

Nehemiah 6:16When our enemies and the surrounding nations heard about it, they were frightened and humiliated. They realized this work had been done with the help of our God.

Self-confidence that rises based on misreading circumstances is bound to fall short of what we need to face reality.

Jeremiah 9:23-24This is what the Lord says: “Don’t let the wise boast in their wisdom, or the powerful boast in their power, or the rich boast in their riches. But those who wish to boast should boast in this alone: that they truly know me and understand that I am the Lord who demonstrates unfailing love and who brings justice and righteousness to the earth, and that I delight in these things. I, the Lord, have spoken!”

When self-confidence is based on our own wisdom and understanding, our power and abilities, or our riches and resources, it is resting on shaky ground. The best confidence is actually confidence in the Lord and what he can do.