Becoming exposed to or infected with a microbe does not necessarily mean developing noticeable disease. Explain.

An infectious microbe is able to cause a disease only if the immune system of the infected person is unable to put proper defence against it. Many persons have strong immune system or have acquired immunity against the pathogen or the intensity of pathogenic attack is quite mild. As a result, despite exposure to infective microbe, the person will not catch the disease. This will make the person stay healthy for long.