In all relationships, and traditional relationship advice there is a very old expression that goes «Why buy the cow if you can get the milk for free». (massimomarinoauthor.com)
There's a useful old expression: We judge others by their actions, but we judge ourselves by our intentions. (lawyerist.com)
This folksy variation of older expressions such as «leave well alone» or «let sleeping dogs lie» appears to have originated in the USA during the 20th century. (bookbrowse.com)