今天的谚语：

Wisdom sets bounds even to knowledge.

Friedrich Nietzsche (1844-1900)

答案详解：

a nine days' wonder 昙花一现

When something only lasts for very short time, we use a nine days' wonder：“昙花一现”在中文里是个成语，它在英文中的表达也是约定俗成的。你可以用 a nine days' wonder，也可以用 a flash in the pan，你甚至可以说 last briefly¹。

Example:

The good days were only a nine days' wonder. 那好时光却只是昙花一现。