I don't think earning 3 million won net per month is that difficult.

It is difficult to earn that much while strictly adhering to a 5-day work week, working 8 hours a day, maintaining work-life balance, and taking all the rest you want.
However, even people without any special skills, such as those working in apartment security (not security guards, but 3-shift security), can take home about 3 million won net by receiving 1.5x night shift allowances and working on weekends while resting on weekdays.
Of course, it is hard to have your day and night swapped and difficult to work on weekends. But, quite literally, you can't say that security personnel have exceptionally outstanding skills. I am writing this because I feel that 3 million won net is being overrated in a world where you can make money doing anything as long as you have the will.