Định Nghĩa và Ý Nghĩa của "not know B from a battledore"

What is the origin of the proverb "not know B from a battledore" and when to use it?

The origin of the proverb "not know B from a battledore" can be traced back to the early 18th century in England, where "battledore" referred to a type of paddle used in the game of battledore and shuttlecock, an early form of badminton. The saying highlights a person's inability to differentiate between simple or fundamental things. It serves as a reminder to recognize and admit when one lacks understanding in a particular area, rather than pretending to know something one does not.