Try everything, leave nothing unattempted.
The phrase has been used since the mid 1500s in its present form, but it originated in ancient Greece, in a tale told by Euripides.
The tale goes this way: When Xerxes made war on the Greeks, and was vanquished at Salamis, he went away but left Mardonius behind to carry on the war in his name. When the latter was also beaten in 477 BC and had fled, a rumor began that Mardonius left an immense treasure buried in the ground near his tent.
Excited by this prospect, Polycrates bought that piece of ground. However, when he failed to find the treasure, he consulted the oracle of Delphi. Apollo replied in these words, “Leave no stone unturned.” As soon as Polycrates had turned over every stone, he found a great hoard of gold.
Another possibility is that the metaphor comes from people who hunt for crabs along the seashore. The crabs usually lie hidden under rocks, which must be turned over in order to find the treasure. But I like the Greek myth better, simply because it’s more interesting.
The phrase is often used, as in “We will leave no stone unturned to find the cure for cancer.” But I prefer something that was written by Edward Bulwer Lytton, English Politician and Playwright, who also famously wrote, “It was a dark and stormy night”:
“To find what you seek in the road of life,
the best proverb of all is that which say;
Leave no stone unturned.”
You never know what you’re going to find under a stone, though. A secret? A treasure? I love mysteries!