Viktor Frankl was a Jewish psychiatrist who spent three years during World War II living under unspeakable circumstances in several of the most notorious Nazi concentration camps.
While imprisoned, Frankl realized he had one single freedom left: He had the power to determine his response to the horror unfolding around him.
And so he chose to imagine.
He imagined his wife and the prospect of seeing her again. He imagined himself teaching students after the war about the lessons he had learned.
Frankl survived and went on to chronicle his experiences and the wisdom he had drawn from them.
"A human being is a deciding being," he wrote in his 1946 book, "Man's Search for Meaning," which sold more than 10 million copies. "Between stimulus and response there is a space. In that space is our power to choose our response. In our response lies our growth and our freedom."