Happiness is a question of choice for the most part but it partially depends on a combination of three variables: health, the people that you have around you and money.
Of the three mentioned, health has to be the most important because without it, no one can enjoy a fulfilling life. When you posess health, anything and everything is possible whereas lack of it can prevent you from having good quality friends to spend time with and ideas or energy to earn money.
That is why it is crucial to preserve a good state of health both physically and mentally because prevention is easier than treatment and once lost, health can be hard to gain back.
