Why did eisenhower choose to write a failure message prior to the d-day invasion?

Operation Overlord was a massive campaign—an invasion of 4000 ships, 11,000 planes, and nearly 3 million men—that was launched on June 6, 1944. Despite a year of strategizing and a boatload of confidence, Eisenhower had a quiet plan in case his mission failed. If the armada couldn’t cross the English Channel, he’d order a full retreat. One day before the invasion, he prepared a brief statement—just in case:

I saw a rock underneath a tree.