Du Fu wrote poems to praise the teacher.

Du Fu

Good rain knows the season, when spring comes.

Sneak into the night with the wind, moisten things silently.

The wild path is dark, and the river is bright.

Look at the red and wet place, the flowers in Jinguancheng are heavy.

People often use Du Fu's "sneak into the night with the wind, moisten things silently." In a word, it describes the cultivation of students by teachers in obscurity and imperceptibly.