Stockdale paradox:

http://jobtransition.net/wp-content/uploads/2011/07/The-Stocksdale-Paradox-from-Good-To-Great.pdf

From Collins: "Good to great"

The name refers to Admiral Jim Stockdale, who was the highest ranking United States military officer in the “Hanoi Hilton” prisoner-of-war camp during the height of the Vietnam War. Tortured over 20 times during his eight-year imprisonment from 1965 to 1973, Stockdale lived out the war without any prisoner's rights, no set release date, and no certainty as to whether he would even survive to see his family again. He shouldered the burden of command, doing everything he could to create conditions that would increase the number of prisoners who would survive unbroken, while fighting an internal war against his captors and their attempts to use the prisoners for propaganda.

“I never lost faith in the end of the story,” he said, when I asked him. “I never doubted not only that I would get out, but also that I would prevail in the end and turn the experience into the defining event of my life, which, in retrospect, I would not trade.

 “Who didn’t make it out?”
“The optimists. Oh, they were the ones who said, ‘We’re going to be out by Christmas.’ And Christmas would come, and Christmas would go. Then they’d say,‘We’re going to be out by Easter.’ And Easter would come, and Easter would go. And then Thanksgiving, and then it would be Christmas again. And they died of a broken heart.”

Another long pause, and more walking. Then he turned to me and said, “This is a very important lesson. You must never confuse faith that you will prevail in the end—which you can never afford to lose—with the discipline to confront the most brutal facts of your current reality, whatever they might be.”

To this day, I carry a mental image of Stockdale admonishing the optimists: “We’re not getting out by Christmas; deal with it!”