One day, poet who greatly admired Wen Yu Ke's drawings wrote a poem about him. The poem contained the phrase, "与可画竹时，胸中有成竹“. This phrase is where the idiom "胸有成竹" (xiong you cheng zhu) originates, meaning that Wen Yu Ke had the image of the bamboo in his mind when he was drawing the bamboo. However, when people use this idiom, they do not mean the literal translation. Instead, the idiom is used to suggest that when someone does something, they are determined and have a solid plan for whatever they set out to do.
Read more about the idiom here.