Because the body is material, his natural tendency is to be attracted by the varieties of the material world. Thus the living entity suffers the miseries of material existence

Expressions researched:
"Because the body is material, his natural tendency is to be attracted by the varieties of the material world. Thus the living entity suffers the miseries of material existence"

SB Canto 7

In this way the conditioned soul living within the body forgets his self-interest because he identifies himself with the body. Because the body is material, his natural tendency is to be attracted by the varieties of the material world. Thus the living entity suffers the miseries of material existence.

SB 7.13.28, Translation and Purport:

In this way the conditioned soul living within the body forgets his self-interest because he identifies himself with the body. Because the body is material, his natural tendency is to be attracted by the varieties of the material world. Thus the living entity suffers the miseries of material existence.

Everyone is trying to be happy because, as explained in the previous verse, sukham asyātmano rūpaṁ sarvehoparatis tanuḥ: when the living entity is in his original spiritual form, he is happy by nature. There is no question of miseries for the spiritual being. As Kṛṣṇa is always happy, the living entities, who are His parts and parcels, are also happy by nature, but because of being put within this material world and forgetting their eternal relationship with Kṛṣṇa, they have forgotten their real nature. Because every one of us is a part of Kṛṣṇa, we have a very affectionate relationship with Him, but because we have forgotten our identities and are considering the body to be the self, we are afflicted by all the troubles of birth, death, old age and disease. This misconception in materialistic life continues unless and until one comes to understand his relationship with Kṛṣṇa. The happiness sought by the conditioned soul is certainly only illusion, as explained in the next verse.