The coronavirus is dangerous because it has a long incubation period where people are asymptomatic or mildly ill but highly contagious. It enters human cells through ACE2 receptors in many organs, including the lungs, where it can cause damage and symptoms like shortness of breath. While most cases are mild due to an innate immune response, the virus's ability to spread silently during the incubation period is why it has caused a global pandemic.