Lack on human affection, talking through screens, avoiding looking into anyone's eyes, growing up being told not to feel anything, lack of physical activity.  There's a host of real reasons for depression. That being said, the majority of people aren't clinically depressed, they're just unhappy at times and thus "I'm depressed" as in not dealing with what human feelings they're experiencing at the time.  I have a whole lecture on why everyone claims to have some type of mental illness, but it's too much for this type of forum.  The gist is we don't know how to feel.