Self-made and self-sufficient people live in a fantasy world, empty of the reality of God. In contrast, the poor in spirit are deeply aware of being God-made and God-sufficient:
Matthew 5:10, Philippians 2:8-9, Luke 6:20, 2 Corinthians 12:9, Psalm 37:11, James 4:10
The Sermon on the Mount is, spiritually speaking, actually the sermon from the valley. It starts low. It starts with those who feel very unlike mountains!