Depression is a serious mental illness. It affects you both physically and mentally and can make even the simplest tasks (like cleaning your room or doing your laundry) seem unbearable. More than 15 million Americans have been diagnosed with depression and are currently living with this illness. Those are just the number of cases that have been been fortunate enough to have been officially diagnosed.
Depression is something you have no control over. It is caused by an imbalance of chemicals in the brain, and there are an infinite number of things that can set off a depressive episode (It is different for everyone). People don't choose to be born this way. People don't choose to have their brains wired like this. People assume that, just because it isn't visible on the surface, that depression "isn't that big of a deal"... but for these 15 million+ Americans, it is. These people aren't being dramatic. These people aren't doing this for attention. These people are struggling, and oftentimes, these feelings become too much for a person to take. Suffering from depression is not a choice, and neither is happiness.
You have no idea how degrading it is to be struggling with depression (or any other mood disorder or mental illness) and constantly being told:
"Just smile more, you'll feel better."
"I don't understand why you choose to act like that."
"Happiness is a choice... you control how you feel."
"I can't deal with you and your moodiness anymore..."
"Stop being so dramatic about it."
"Come on, it's not THAT bad just get over it."
... and the list goes on.
If happiness were a choice, I would choose to be happy every day. But, it isn't a choice. This isn't some video-game where we all get to pick out our character attributes and be "whatever we want to be". This is real life. We have to work with what we've been given, and try to get better. All you can do sometimes is try.
People who are suffering from depression are not "broken". They don't need or want your sympathy or your pity. Just don't belittle someone else because of how they feel. Be respectful of other people and what they're dealing with. Happiness is not a choice, and this cliche idea needs to be broken down and stopped from being overused by people who have no idea what it's like to suffer from any sort of mental illness.
Remember, we're all fighting our own demons. Don't make anyone else's battle harder.