Here's why:
* Figurative meaning: Idioms often have a metaphorical or figurative meaning, which differs from the literal meaning of the words. For example, "kick the bucket" means "to die," not literally kick a bucket.
* Fixed expression: Idioms are typically fixed expressions, meaning the words cannot be changed or rearranged. Saying "kick the pail" instead of "kick the bucket" would change the meaning or make the phrase nonsensical.
* Culturally specific: Idioms are often specific to a particular language or culture, and their meaning may not be understood by people from other cultures.
In essence, idioms are like little puzzles that require understanding the context and the shared cultural knowledge to decipher their meaning.