A positive mental attitude is an incredibly important part of survival, but a naïve or foolhardy attitude can be dangerous. It’s a phenomenon known as the Stockdale Paradox, named after Admiral James Stockdale, the highest ranking American prisoner of war in Vietnam. In the POW camps, optimists were the first to die, Stockdale told author Jim Collins in his bestselling book Good to Great. Optimists were always hoping to be released at Thanksgiving or Christmas, but were crushed when those holidays passed and they were still imprisoned. They couldn’t stand the disappointment and gave up fighting, Stockdale said. Soon after, they died. In the toughest situations, experts say, you should exercise “realistic optimism.” That means combining a blunt factual appreciation of your predicament with steadfast hope that things will turn out okay.