From 《
世说新语》: when the boy
王献之 remarked on a game, the retainers watching dismissed him with
管中窥豹,
时见一斑, 'peering at a leopard through a tube, he glimpses one spot at a time'. Modern speech often turns it round as
管中窥豹,
可见一斑: a single spot is enough to picture the whole.