Actually,people are sad all the time because life is unfair,they are bored and with no goals in life,they're depressed of being victims of some unfair stuff,or simply,because they don't know how to smile.
What? does it seem strange to u that they are sad while through the globe there is so much misery, pain, unfairness? There are wars going on, big earthquakes(japan), hunger, hatred and crime everywhere, suicides. They are not exactly perfect for keeping your happiness on the maximum. :( And all these people get a taste of life's unfairness and sadness.
Everyone feels sad at times. Sad feelings can be mild of strong of in between. How sad u feel can depend on the situation that's causing the sadness and how you're coping with it.
Sadness is a natural human emotion. Like other emotions, sad feelings come and go. Some sad feelings last only a moment, some last longer. When sad feelings ease away, a happier mood can take their place.
-When things don't go your way. -Your feelings get hurt. -You lose something special. -You miss someone. -You hear about something sad. -Someone dies. -A problem makes u sad.
That's just the way they are. They may face problems in their life like getting bullied, having depression... Etc. I can be sad and sometimes I can be happy. I'm sad because I have to go to school but I'm happy cause I don't have Math today :3