Salt

The word salary comes from salt. In ancient Rome, soldiers' salary is salt. For what people fight with their lives? For salt. 

In nature, salt is a very scarce resource. In many places, hunters put salt in the wild as a bait to attract animals.  

Only in modern society, salt becomes cheap and abundant. Many people indulge in salt and eat too much salt. As a result, low salt diet becomes the signal of healthy diet. Sometimes there is very little salt in a family diet. However, salt is an essential ingredient to support normal physiological processes. Lack of salt will make people lethargic. For people at growing stage, lack of salt will stunt people's growth.