"McNamara, Johnson's Defense Secretary, finally admitted (in his old age) that they were mistaken about the Vietnam War and shouldn¹t have been fighting it at all. Serious lies and untruths will always surface. Sometimes it is quick and still others require years to see the light. I believe the Kennedy assassination conspiracy theorists will WAIT UNTIL THE COWS COME HOME to hear the truth of that incident."
(Joe Lincoln - in Salesmenship - June 2002)
Did you know?
Did you know?
This idiom comes from the late 16th century and means a long, long time.
Cows took a long time to come from the fields to the barn, so when you use this expression you're describing a long time or passage.
You may also hear the idiom "donkeys' years" which means roughly the same thing.
"It can take donkeys' years to learn to speak a foreign correctly!"