Most people who are in pain are angry all the time
while some levels of pain made some go quiet and distance...
you are right that everyone has a demon to fight, not all people who smile are happy and there are people you think are living good lives which is just a disguise because they are going through worse but they choose not to let others see that part of them, cos revealing it won't solve their problem anyway...
This is why I don't like it when some people get angry that someone doesn't help them because they think he is doing fine, what if he is in a difficulty positions than you asking for help bt he just choose to bear it alone...
take care of yourself man, life is cruel but keep fighting