εἰστέον

From LSJ

ὁ γὰρ μανθάνων κιθαρίζειν κιθαρίζων μανθάνει κιθαρίζειν → he who is learning the harp, learns the harp by harping

Source

Spanish (DGE)

hay que conocer Ael.Dion.ε 23.