Idioms can be a curse for foreign language learners. First, it’s not obvious what they mean. Secondly, we don’t know where the expression comes from and thirdly, even if we have a similar concept expressed by an idiom in our own language it uses completely different language to do so. A common example in German is dienst is dienst und schnaps ist schnaps, which translates literally as work is work and schnapps is schnapps (an alcoholic drink). However, the comparable expression in English is Don’t mix business and pleasure. Not obvious to a speaker of German learning English and definitely not to an English speaker learning German. This is why appreciating the etymology of words and phrases to understand how they came to mean what they mean today is an important linguistic skill, as illustrated in Caroline Taggart’s book about the origins of many common expressions used in everyday English.