The "good old days."

Is it a flaw in human nature, or an evolutionary defense mechanism that we normally tend to remember the good and repress the bad? I'm feeling especially nostalgic for the optimisim of the late years of the last century. Business booming, the human race more aware of the need to preserve the environment. Asia modernizing, India awakening, the Eurozone, the end of Apartheid, travel and technology, peace and prosperity. What a wonderful world the 21st century was going to bring us! Sigh...