The feat, from the perspective you describe, isn't that remarkable. Humanity has tons of projects that meet these exact standards throughout our history:
> We built something meant to work for decades, knowing the people who launched it would never see the end of the story.
> We pointed a metal box into the dark with the assumption that the future would exist and might care.
> It’s proof that humans will build absurdly long-horizon projects anyway, even when the ROI is almost entirely knowledge and perspective.
The pyramids, the Bible, governments, or even businesses [0] are all human constructs that last way beyond their creators (and their intention), with and without their creator's intention.
> we ever build a civilization stable enough to think in centuries without collapsing every few decades.
The challenges to even get close seem insurmountable. At that speed, microscopic grains of dust hit like bullets. It's not like the nearest is much of a prize - we know that the Centauri system is likely inhospitable and that Tau Ceti has an enormous debris field.
> We built something meant to work for decades, knowing the people who launched it would never see the end of the story.
> We pointed a metal box into the dark with the assumption that the future would exist and might care.
> It’s proof that humans will build absurdly long-horizon projects anyway, even when the ROI is almost entirely knowledge and perspective.
The pyramids, the Bible, governments, or even businesses [0] are all human constructs that last way beyond their creators (and their intention), with and without their creator's intention.
> we ever build a civilization stable enough to think in centuries without collapsing every few decades.
This is a valid point though
[0] - https://en.wikipedia.org/wiki/List_of_oldest_companies