Well, you should differentiate between "normal-people" depressions and "clinical" depressions.
I suffered from serious depression until my mid-twenties. It made it difficult to function, yet the people around me couldn't understand or relate. I can't tell you how many times I was accused of "just being lazy". My mother once said to me, "I know you're not faking because no one would deliberately be this miserable." You absolutely have to treat this "like a broken leg" because it is a real illness that won't just go away on its own. I did that and eventually found help that worked for me. Except for one nightmare-ish three day recurrence (I was so scared) I've never suffered from it again.
Since then, I have had normal depression once or twice. This is what people meant when I tried to tell them about my sickness before and they would say, "Everyone feels depressed from time to time." (Oh how that sucked.)
Now I get it. Everyone does feels depressed from time to time, due to reasons. Something bad happens, or some condition is deeply unsatisfying in your life and you feel bad. That's totally normal and part of navigating life. (To me, having dealt with the monster for so many years, normal depression is almost cute. Even though it still sucks. It's the difference between a scratch and a tooth-ache.)
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edit: I just realized that this is why I couldn't understand Wood's actions. Given my history I wouldn't let anything send me back to the pit. Not even my most cherished project.
Thanks folks who responded. Warm regards.