A fire at a third-party datacentre - would you be happy to lose your job for that?
SK has its own local tech so that it never needs to 'take back control' of its digital borders. They used to slow access to global tech to promote the local hangul version, causing havoc for tourists. SK tech companies play by SK rules. Unfortunately, having all your eggs in one small nationalist basket like that makes your tech much less resilient than global tech.
No tech is 100% and in general, digital is less resilient than physical. Politicians do not understand this and throw a hissy fit when everything stops working, ordering companies to be perfect. But tech will always go down. Upgrades, fires, hackers, workmen, angry Australian wildlife, the CIA cutting your cables.
Always have an old school 'Plan B'. Pens, pencils etc. Carry cash to get you home, have some in for when the internet banking and e-payment systems tank, and employ people who can add up (or use a calculator). The more dependent we are on tech, the more damage there will be when (not if) it goes down.