<p>The immune system has an attack/defense function, but at the same time it is possible that its primary function is much more physiological than a war-related function. Perhaps the protective function against microorganisms is the exception to the rule once we are much more tolerant than responsive to foreign entities. Have you ever stopped to think that in the space we call the human body there are more non-self entities, such as commensal microorganisms, than there are self entities? There is also the context of pregnancy in which there is a need to tolerate proteins derived from a non-self genome. Or even the tissue remodeling functions that are performed by macrophages and are not necessarily related to protection against microorganisms. This review focused on the role of the immune system as general, and discusses the spectrum of immune functions with an emphasis on the analogy about the state of human nature: is the immune system good or bad by nature, in an interaction with microorganisms’ perspective?</p> Graphical Abstract <p></p>