The virus affects everyone so differently because there are many factors to people's health. Many people that have pre-existing health conditions are severely more at risk than those who don’t. The immune system response of  different people affects the severity of the virus's impact on them. Seeing as the Corona virus in an unfamiliar virus the immune system is reacting for the first time so an over the top response can result in the body attacking itself but an inadequate response allows for the virus to continue to spread and sometimes the response is just right and the person is perfectly ok.