It's human nature to be optimistic, it is an evolutionary thing since too much realism, let alone pessimism, about possible future problems actually hampers our success in surviving and thriving. As you say OP, if we all focused solely on the negative we would become so depressed and dysfunctional that we would bring major problems upon ourselves just as a result of that outlook. I have suffered major mental health problems myself so I know only too well.
I completely understand why people feel hopeless, why the current situation is daunting, and I really sympathise, and share a lot of the worry. I am not super positive or resilient at all.
I do agree we should try to resist the doom though, it is a good coping strategy to not think too far ahead, to try and focus on the positive. There is a purpose in venting your feelings and acknowledging difficulties, but continuing to do so endlessly won't get any of us anywhere.
Never underestimate the power of human ingenuity and resilience, we have come through some appalling things and even in the aftermath of disaster people go out to rebuild.
By the way, i am fairly confident there will be a vaccine. It may not give total immunity, it may need boosters, and it may be some time after we get it that measures can significantly ease, but it will come and it will change things a lot. Imo of course, but my opinion is based on listening to multiple experts so
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I think there will be huge appetite for returning to normal as much as possible and we will see so much new enterprise spring up, including in the arts.