巧妇难为无米之炊（巧婦難爲無米之炊）　

◎ 巧妇难为无米之炊 qiǎofù nán wéi wú mǐ zhī chuī

[the cleverest housewife can’t cook a meal without rice—one can’t make bricks without straw] 比喻主观再努力而客观条件不具备,也难成事