The biggest difference seems to be whether it can be easily replaced by someone else. Representative high-income jobs in Korea are celebrities and CEOs. They have their intangible values, making it difficult for others to take over their work. Jobs that should pass the test to get a certificate also usually earn a high income. For example, doctors, accountants, and lawyers must pass tests to obtain a license. Their high income can be granted because the number of workers remains constant due to tests.