Arthur C. Brooks in The New York Times:
ABD AL-RAHMAN III was an emir and caliph of Córdoba in 10th-century Spain. He was an absolute ruler who lived in complete luxury. Here’s how he assessed his life: “I have now reigned above 50 years in victory or peace; beloved by my subjects, dreaded by my enemies, and respected by my allies. Riches and honors, power and pleasure, have waited on my call, nor does any earthly blessing appear to have been wanting to my felicity.” Fame, riches and pleasure beyond imagination. Sound great? He went on to write: “I have diligently numbered the days of pure and genuine happiness which have fallen to my lot: They amount to 14.”
Abd al-Rahman’s problem wasn’t happiness, as he believed — it was unhappiness. If that sounds like a distinction without a difference, you probably have the same problem as the great emir. But with a little knowledge, you can avoid the misery that befell him. What is unhappiness? Your intuition might be that it is simply the opposite of happiness, just as darkness is the absence of light. That is not correct. Happiness and unhappiness are certainly related, but they are not actually opposites. Images of the brain show that parts of the left cerebral cortex are more active than the right when we are experiencing happiness, while the right side becomes more active when we are unhappy.