sure (as sure as eggs is eggs )

英语词源

sure (as sure as eggs is eggs )确信无疑地

as sure as eggs is eggs运用了明喻的手法，指“确信无疑地”。如：

He’ll be late again, as sure as eggs is eggs.

毋庸置疑，他又要迟到了。

可以确定的是，这一表达与鸡蛋毫无关联。它是数学概念中“X等于X”的变体，即“某事确信无疑，如同X就是X”。

——摘自《单词的历史：英语词源漫谈》