不知天高地厚

1. • not to know the immensity of heaven and earth
2. • an exaggerated opinion of one's own abilities

Character by character

• 不(bù)no
• 知(zhī)know
• 天(tiān)day
• 高(gāo)surname Gao
• 地(dì)earth
• 厚(hòu)thick