Let sleeping dogs lie dog bed

‘Let sleeping dogs lie’ derives from the long-standing observation that dogs are often unpredictable when they are suddenly disturbed. Geoffrey Chaucer was one of the first to put this notion into print, in Troilus and Criseyde, circa 1380, although the belief itself may well be much older:

“It is nought good a slepyng hound to wake.”

The expression may have started as a warning about the risk of waking a potentially dangerous animal, but it later turned metaphorical.

By the time it became established as a proverb its meaning had ‘leave well alone’, or as we might have it in the 21st century, “if it ain’t broke don’t fix it”.

The cautionary phrase was well enough known by the 16th century for it to have been included as a proverb in John Heywood’s definitive A Dialogue conteinyng the nomber in effect of all the Prouerbes in the Englishe tongue, 1546:

It is euill wakyng of the slepyng dog.

At this point I ought to mention the 18th century British