Take fireflies for example. Try to imagine their beauty, the evanescent beauty of their lives, which don't even last a week.Female fireflies flash their lights only to have intercourse with the males; males twinkle just to have intercourse with the females. And once their mating has finished, they die. In short, their reproductive instinct is the single, absolute reason for fireflies to live. In that simple instinct and their simple world, no kind of sadness can intervene. This is precisely why fireflies are so fleetingly beautiful.