数典忘祖

shǔdiǎn-wàngzǔ

[give all the historical facts except those about one's own ancestors; forget one's ancestors and ancestral tradition] 据《左传》记载, 春秋时晋国大夫籍谈没有回答好周天子的提问而被周天子讽刺为"数典而忘其祖"。 后比喻忘掉自己本来的情况或事物的本源