What does it mean to drive the donkey to the shelves?

Metaphor is an impossible goal. This idiom means that it is difficult to accomplish something, or do an impossible thing, or an impossible goal. It comes from an old legend in China, which tells that a shepherd was asked to drive a donkey without legs to the shelf, and he could not finish the task. Therefore, this idiom is used to describe a very difficult thing or an unattainable goal.