with complete confidence 胸有成竹

胸有成竹，汉语成语，本意是指“在文艺创作开始前，艺术形象已在头脑中生成（have an image of the art in one's mind prior to artistic creation）”。后比喻在做事之前已经拿定主意，有自信，可以翻译为“have had ready plans [designs] in one's mind；with complete confidence”。

例句：

所有的答案他都胸有成竹。

He had all the answers off pat.

她对自己的立场不再胸有成竹。

She was no longer sure of her position.