Depression - real depression - is obviously a debilitating thing. But some negativity, can actually be a good thing. It can make you more realistic, it's usually found in more intelligent people in my experience - in fact ever since the time of Aristotle people wondered why creative thinkers and artists all tend to be "melancholy" (black bile) and "saturnine" (governed by the planet Saturn, i.e. Capricorns). So I think melancholy/negativity is like salt: too much of it can ruin a dish, but just the right amount can make it better. Just my 2 cents, obviously this doesn't negate anything you said in the video!