得鱼忘筌dé yú wàng quán

筌是用来捕鱼的器具。得到了鱼，就忘掉筌。比喻达到目的以后就忘了赖以成功的东西。

例筌者所以在鱼，得鱼而忘筌。——《庄子·外物》

英forget the means by which the end is attained; forget the trap as soon as the fish is caught;