My preferred version: do what you can, don't sweat it.
To phrase it negatively, it's a kind of selfishness / indifference. But it's not "I don't care", but more "it is what it is".
I see some people accept with serenity the things that cannot be changed, but then have no courage to change the things which should be changed because they have no wisdom to distinguish the one from the other.
An easy read that dives into stoicism, a similar mindset, within the context of running the Roman Empire.
Great read.