The article refers to the idiom menyat' (smenyat') shilo na mylo , which means 'to make a bad choice; to choose the worst from several bad things'. After having critically evaluated the existing hypotheses about the origin of this idiom, the authors propose their own version, based on the data of Russian folklore and dialects. The authors suggest that the idiom should be considered in a general linguistic context formed around the binomial shilo-mylo . There are several reasons for attraction of these two words. The words awl and soap designate the items which are indispensable for housekeeping and the most common things in small shops selling household goods. Besides this everyday contiguity of the items, there is a phonetic resemblance of the words. They function in the frames of a popular reduplication model, on the basis of which constructions with initial letters sh and m are created (i. e. shury-mury). A wide range of meanings can be designated by this binomial (semantics of something necessary or, on the contrary, of something useless, meanings of greed, slyness, etc.). The components of this pair create different formal correlations (shilo-mylo, ot shil 'nogo do myl 'nogo, shil 'tse da myl 'tse, shil 'e-myl'e, etc.). They function in constructions with predicates, for example, with the verbs perevesti (svesti) and menyat' (promenyat') . With these verbs, the two words are part of two phraseological models existing in popular speech: on the one hand, idioms with the verbs pere-vesti and svesti , meaning futile labor and vain efforts (svest' na myl 'nyy puzyr' ), on the other hand, idioms with the verbs menyat', promenyat' , meaning useless and inadequate exchange (promenyat' byka na indyka). On the assumption of the authors, the idioms svesti (perevesti) shilo na mylo appeared earlier than the idioms with the semantics of exchange.