One of the mysteries of the English language finally explained.
With material from the sides interchanged with that in the middle; specifically (with reference to a worn sheet of bed linen) by being cut down the centre and resewn with the two halves interchanged, so that what were the sides become the middle, and the sheet's useful life is extended.
Of a worn sheet of bed linen: cut down the centre and resewn so that the sides and middle are interchanged.
Mid 19th century; earliest use found in New York Spectator. In some forms from the plural of side + into + middle.
sides to middle/ˌsʌɪdz tʊ ˈmɪdl/
In this article we explore how to impress employers with a spot-on CV.