And the most important thing about idioms is their meaning. This is why a native speaker does not notice that an idiom is incorrect grammatically. If the source of an idiom is known, it is sometimes easier to imagine its meaning.
Idioms come from all different sources — from the Bible to horse racing, from ancient fables to modern slang. Sometimes famous authors and storytellers such as Homer, Aesop, Geoffrey Chaucer, or William Shakespeare made them up to add spark to their writings.
The authors were popular, so the expressions they created became popular.
Many idioms include parts of the body, animals, and colors. Some became popular because the rhyme (snug as a bug in a rug) or have alliteration (spick and span). Some idioms originated as colloquialisms (informal speech) or slang (casual, playful, non-standard language). Some were well-known proverbs and adages (short sayings that express practical, basic truths). Some popular idioms began as folksy saying used in particular regions of the country and spoken in local dialects. Many came from other countries. Some idioms go back in time to the ancient Greeks and Romans, thousands of years ago. Others are more recent.
So idioms come from all over the place
such as famous authors, ancient fables, religious sayings, and modern slang. Word experts who study origins of idiomatic expressions don't always agree on exactly where each one came from.
In this work, I've included the most accepted explanations.