Despite your strong objections, someone you know is still using a Windows operating system that predates Windows 10 and has reached the end of its extended support period. The software he usually uses on it is still functional, and an antivirus is installed. Why should he upgrade to a newer operating system?

Operating systems (OS) has their own life cycle. They are launched, grow, maturity (mainstream support), decline (extended support), and reach end-of-life (EOL), which signifies no support. The previous Windows operating system, Windows 8.1, finished mainstream support on January 9, 2018, and extended support will end on January 10, 2023. Other than security patches, the end of mainstream support means no more updates. When extended support ends, there is no longer any support, including security updates and patches. Essentially, if (when) a vulnerability is discovered by a hacker, the user of an out-of-date operating system is vulnerable to attacks. Applications may continue to function normally, however upgrades may not be compatible with the operating system. The operating system will not stop working by itself, but if a problem arises, there will be no official help available.