From 《
礼记·
学记》 (Li Ji, Record of Learning, compiled late Warring States / early Han, ca. 2nd c. BCE), one of the earliest systematic treatises on education in the world. Full passage:
独学而无友,则孤陋而寡闻 (If one studies alone without companions, one becomes narrow and ill-informed). The line justifies the communal school as essential to real learning.