In every organ there are hundreds of thousands of cells and their activity is subordinated to the general tasks of the organ. Therefore, the cells function in concert, but in different modes (simultaneously or alternately). Such modes of activity allow you to change the performance of the body, reducing or increasing it in the interests of the body.
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.