巧婦難為無米之炊（巧婦難爲無米之炊）　

◎ 巧婦難為無米之炊 qiǎofù nán wéi wú mǐ zhī chuī

[the cleverest housewife can’t cook a meal without rice—one can’t make bricks without straw] 比喻主觀再努力而客觀條件不具備,也難成事