In Swedish, this is a common phrase used to describe a situation where somebody has bought something without first fully examining it. And it proves to be a costly mistake. It’s also used to describe situations where somebody says yes to something without really knowing what it is – to their detriment. The expression ‘köpa grisen i säcken’ is the equivalent of the little-used English phrase ‘to buy a pig in a poke.’
But where does the expression come from?
Well, it dates back to the late Middle Ages when livestock was sold in the market places. Small animals were transported in sacks so as to make it easy to carry them. When you bought an animal, if you didn’t look in the sack, you might be in for a big surprise when you got home. You thought you bought a piglet, for example, but on opening the sack you realize it contains a rat or a cat.
It’s a bit like voting for a person or a party without fully understanding their politics and then being shocked afterwards. You really shouldn’t have bought that pig in the sack.