The mind is a system that operates due to an interaction between its various components and between it and the body and between it and the surroundings.
These components are:
Any purposeful action we undertake takes place due to a harmonious interaction between these mental components.
It is thus necessary that all parts of the mind work in harmony and maintain the internal balance. It is also important that the balance is maintained between the mind and the body as well as between the mind and the surroundings. E.g. if one is running fever, one cannot expect to visit the theatre even if one wishes to. And that will make us unhappy as our desire has not been fulfilled. Or if there is heavy rain with transport difficulty, one would not like to risk an outing outside. It might make us curse the weather gods for interfering in our desire. This small example illustrates how small and sometimes inconsequential factors become important in maintaining our mind in a state of health.