Because of the material body, the living entity is subjected to many tribulations.

SB 4.29.23-25 P Talks Between Narada and King Pracinabarhi  
In the Vedas it is stated: asango'yam purusah. The living entity is actually separate from material existence, for the soul is not material. In Bhagavad-gita it is also said that the living entity is the superior energy, and the material elements--earth, water, fire, air and so on--are the inferior energy. The material elements are also described as bhinna, or separated energy. When the internal or superior energy comes in contact with the external energy, it is subjected to so many tribulations. In Bhagavad-gita (2.14) the Lord also says, matra-sparsas tu kaunteya sitosna-sukha-duhkha-dah: because of the material body, the living entity is subjected to many tribulations brought about by air, water, fire, extreme heat, extreme cold, sunshine, excessive eating, unhealthy food, maladjustments of the three elements of the body (kapha, pitta and vayu), and so on. The intestines, the throat, the brain and the other parts of the body are affected by all kinds of diseases that are so powerful that they become sources of extreme suffering for the living entity. The living entity, however, is different from all these material elements. The two types of fever described in this verse can be explained in contemporary language as pneumonia and typhoid. When there is an extreme fever in the body, there is typhoid and pneumonia, and they are described as Prajvara. There are also other miseries created by other living entities. The state exacts taxes, and there are also many thieves, rogues and cheaters. Miseries brought about by other living entities are called adhibhautika. There are also miseries in the form of famine, pestilence, scarcity, war, earthquakes and so on. These are caused by the demigods or other sources beyond our control. Actually there are many enemies of the living entities, and these are all described to point out how miserable this material existence is.