Government policy, government policy government policy and a few other things, in my view. In south Korea, they got their first case very early but still they got a good test up and running in about a week and got a full blown test track trace and quarantine system up within a few more weeks. So they never locked down nationally.
They had a bit of help, but I think that is much less effect. They had a scare with SARS and MERS which we avoided so their population had experience and were willing to do the right thing. They nearly all wear masks in the street, before covid because of previous experience. When a secretive Christian sect caused thousands of cases in one city with mass services. The whole city was not officially locked down but the population did it anyway voluntarily.
They have more mobile phones per head than any other country. (Samsung is south Korean). Their tracing phone app works!
But in other ways they are similar to us: as urban, more densely populated, about equal numbers of citizens, very similar age profile.
But South Korea is not alone, I could point out New Zealand, Taiwan, Singapore, Japan, Germany, Australia all have done better in damage to the economy and deaths too! China too but they are not a democracy. Test , track, trace quarantine is the common thread with these countries.
Brazil, Russia and the USA have made a mess of both economy and covid deaths, like us. I see a similarity between the governments of we four countries. Populism before expertise.
Agreed Italy and Spain have suffered too and do not fit my view.
However I think it is not a balance between health and the economy. Avoid long periods of lockdown and you can have both. Test , track trace quarantine.