Just a figure of speech.
Pot calling the kettle black - I recently learnt the origin of this phrase whilst reading the Spanish novel Don Quixote by Cervantes (Would deffo recommend btw). It referred to the fact that pots and kettles of the time were made of cast iron and got blackened in the fire and is used to suggest that one shouldn't accuse or criticise another of something they're also guilty of. Those who know/pity me or care to indulge in my nerdy side may find this interesting... those that don't... well I would stop reading at this point.
An idiom is a figure of speech that means something different than a literal translation of the words would lead one to believe. For example, "it's raining cats and dogs" is a common idiom in English, but it's not meant to be taken literally: Household pets are not falling from the sky! It's a colourful way of saying that it's raining really hard outside.
Because idioms are such interesting ways to get a point across, they're often seen in literature. In fact, many of the most common idioms we use today were originally coined by great writers as a unique metaphor; then people liked them enough to start using them in everyday conversation.
Many other authors also coined their own idioms or used common idioms in their works to great effect. Idioms often help make dialogue more realistic and make clear a character's personality, education or background. Here are more idioms used in famous works of literature:
I can't do [X] to save my life - This phrase can be traced back to English novelist Anthony Trollope in The Kellys and the O'Kellys. The original version is "If it was to save my life and theirs, I can't get up small talk for the rector and his curate." Here the speaker explains that he's so bad at small talk he couldn't do it even to save his life. It's still used to indicate someone is no good at an activity, often in a self-deprecating way.
Break the ice - This phrase was first used in The Taming of the Shrew. Tranio encourages Petruchio to "break the ice" with Katherine to get to know her, suggesting that he may like her better - and get her to like him. Today this phrase is used to refer to relieving tension or getting to know someone better, usually by making small talk, or a kind gesture to start a new relationship.
Love is blind - First seen in writing in Chaucer's The Canterbury Tales" - For love is blind all day, and may not see" - this phrase means that true love is not superficial and also captures the idea that love can be unexpected or random.
Live off the fat of the land - Though a version of this phrase exists in the Book of Genesis, it's perhaps most famously used in John Steinbeck's novel Of Mice and Men. George tells Lenny they'll live off the fat of the land and have rabbits when they make enough money to stop traveling around for work. The phrase means getting the best of everything without having to work hard for it.
Mad as a hatter - This expression is said to refer to the use of mercury to set felt hats which was thought to drive hat makers crazy. Though the expression predates his work, Lewis Carroll created his Mad Hatter character in Alice's Adventures in Wonderland in reference to this English idiom.
