First, it doesn't matter why this person is/was depressed - it's not our business. Depression, like many other illnesses, is a private matter and only the person suffering has the right to decide who to tell and how much information to share. The fact that Dan Ha is missing does not change this.

Second, while the onset of depression can sometimes be triggered by one or more specific events, the truth is that many cases of depression have no discernible cause. When someone says that "depression needs no reason", they simply mean that there doesn't need to be any specific trigger. Of course there is something underlying the condition - whether it's caused initially by an event, some chemical imbalance in the brain, some combination of the two, or something else that we don't understand yet, the point is that it doesn't have to be caused by "some painful event".

Third, don't assume that depression is a sudden condition. It can creep up on you over time without you realizing it. Or maybe you do realize it, but you do your best to handle it, to get over it on your own, to hide it from others. You can have highs and lows (not to be confused with bipolar or manic episodes), rather times when you feel you are doing better or worse. Maybe you go a week or a month thinking it's gone, only to wake up one morning with depression making itself known again. It can be months or years before anyone else notices, if they ever do. And the ones who do? It's not necessarily your closest friends - it could be a casual acquaintance or a coworker who notices the change.

Depression can consume you. You might think it just means feeling bad, but it can be much worse than that. It can mean feeling dead inside, or not feeling anything at all.

Even when you make a choice to accept help (whether you seek it out or it's forced on you - hopefully before you do something extremely stupid), it can take a long time to recover. Medication often helps, even though we don't no exactly why - yes, we know approximately how the medication changes things in your brain - affecting dopamine uptake, for example, but we don't know why it does it. And it's not a matter of simply going on medication. You have to work with your doctor to figure out the right level for you - and that level might change over time. What worked for a time may be too much later, causing side effects that leave you feeling bad. Adjusting the dose can mean feeling worse for a couple of weeks while you wait for your body and mind to adjust! You sit at work feeling like you're about to fall asleep, and when you try to go to bed you stare at the ceiling for hours. You might be sitting or walking and feel a wave of dizziness. You gain or lose weight, seemingly without changes to your diet or routine. Even though you're not as depressed, it can be hard to go out and do things with people, leaving you feeling isolated.

Therapy can help at times, but it also takes time. You don't just sit down with a doctor and establish trust right away. It takes multiple sessions for a psychiatrist/psychologist to make a diagnosis. And they might not be the ones who can recommend medication either, so you still have to work with another doctor at the same time. Short term therapy ends up lasting for months, or years.

Finally, do you know what can be the worst thing about depression? People who tell you that there's no reason for you to be depressed. People who think it's easy to "stop thinking that way!" People who think that you ought to know why it's happening. People who say "get over it, you've got it good."

Don't believe you know what causes depression because even the people who spend their lives studying it admit that they can't really explain it yet - they can't put together the puzzle because they still haven't even found all the pieces!