i think that are many reasons ,but the most important is that we are humans and that means that we have a mixt of feelings. We can be sad,but it s in our nature to be cheerful,because that it s the feeling that we all fell in some moments. We should be cheerful because we have a life,we have a family,friends,some of us don t have this thinghs,but they are happy anyway because they know that sadness can t take over our life. We should be cheerful in every moment of our life,in every breath,because we are free.
