Who told you everyone is sad?
Right now there is someone laying on a white sandy beach in Cancun, Mexico with the love of their life underneath a thatch hut sipping on a mango daiquiri looking through sunglasses watching the turquoise water waves slowly roll to shore while listening to their favorite music on their iPod and they're thinking to them self:
"Life is good!"
Another person may be getting married tomorrow, someone was just notified of a job promotion or was just hired, another person won the lottery, and someone got approved for their first home loan.....etc
In a world with over 7 Billion people it's highly unlikely that (everyone) is sad at the same time. Misery loves company and people see what they want to see. "Perception is reality".
Truth be told "sad people" try to avoid being around "happy people"!