Any living organism, including humans, cannot live without substances coming from the external environment: food, water and oxygen.

Food is a source of organic, minerals and vitamins.
Water is a necessary condition for life, since it is in water that all biochemical reactions of the breakdown and synthesis of organic substances that are necessary for the cell occur.
Oxygen participates in the processes of obtaining energy by the cell.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.