I won’t take credit for this idea. It was posted on r/worldbuilding but was nuked by the mods for “asking for content”, as usual only after lots of interesting discussion. Anyway…
Unbeatable aliens show up and blow up half the moon as a show of strength. They say that they’ll be back in six months to annihilate the Earth. For the next six months humanity lives in the shadow of their inevitable destruction, with all that mindset entails.
Then when the time finally comes, nothing. No earth shattering kaboom, no heroic last stand, the aliens just never show. What happens next? How do you rebuild?
It’s like your boss coming to you on 4:45 on Friday afternoon and telling you in a super serious tone “I need you in my office first thing Monday morning.” and then completely forgetting about it on Monday.
Is this the one where the neighbors are celebrating the completion of a backyard fallout shelter, then sirens go off and they immediately start fighting because there’s not enough room, then the radio announces it was a false alarm?
No, it’s the one where the aliens that seeded the earth with life come back and announce the imminent destruction of the world due to their disappointment in our development as a species.