From megas (great) and phroneō (to think). To think great things of oneself, to be proud or high-minded. Related to the biblical warnings against overestimating one's importance.
Paul repeatedly warns against thinking too highly of oneself. 'Do not think of yourself more highly than you ought, but rather think of yourself with sober judgment' (Romans 12:3). The antidote to high-mindedness is not self-hatred but accurate self-assessment in light of God's grace. Every gift is received, not earned (1 Corinthians 4:7), so there is no basis for boasting.