The term external is from the early 15c., "overt;" by 1590s as "situated or lying outside," from Latin externus "outside, outward." 

Which is more important, external or internal. It depends. The external environment for business is where the customers pay. The internal environment for business is what runs the business. The external environment for humans is for show. The internal environment for humans is what runs the body. Both business and humans are similar when thinking about internal and external systems. Both internal and external systems are important and each one needs the other. For business, external is the most important. For humans, the internal is the most important. 

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Touchstone of children, ancestor of happiness, sidelines of sadness