seek blood from stone （向石頭求血）緣木求魚

To?do?something?that?is?very?hard?to?accomplish,?especially?when?dealing?with?other?people?in?some?way. 做一些很難完成的事，特指和別人打交道

例句：Getting?a?group?of?toddlers?to?sit?still—it's?like?getting?blood?out?of?a?stone.

? ? ? ? ? 讓一群幼童坐定就好似緣木求魚。