We as humans on earth are currently eating, sleeping, defending and mating at the expense of other living beings because that is what we believe we should do in life:
Religion means to obey the laws of God. That’s all. And if a human being does not obey the laws of God, he is no better than an animal. All scriptures, all religious principles, are meant to elevate man from the animal platform to the human platform. Therefore, a person without religious principles, without God consciousness, is no better than an animal. That is the verdict of the Vedic literature (Hitopadesa 25):
āhāra-nidrā-bhaya-maithunaṁ ca
sāmānyam etat paśubhir narāṇām
dharmo hi teṣām adhiko viśeṣo
dharmeṇa hīnāḥ paśubhiḥ samānāḥ
Eating, sleeping, sex, and defense—these four principles are common to both human beings and animals. The distinction between human life and animal life is that a man can search after God but an animal cannot. That is the difference. Therefore a man without that urge for searching after God is no better than an animal. (Source)
Google: ahara nidra bhaya maithunam ca
The living entity goes through birth, old age, disease and death:
janma-mrtyu-jara-vyadhi-duhkha-dosanudarsanam - the perception of the evil of birth, death, old age and disease (Srimad Bhagavad Gita As It Is, Chapter 13, verses 8-12)
Afterwhich this process repeats itself:
dehino 'smin yathā dehe
kaumāraṁ yauvanaṁ jarā
tathā dehāntara-prāptir
dhīras tatra na muhyati
As the embodied soul continually passes, in this body, from boyhood to youth to old age, the soul similarly passes into another body at death. The self-realized soul is not bewildered by such a change. (Srimad Bhagavad Gita As It Is, Chapter 2, verse 13)
The Lord Himself says that the material universe in which we accept this temporary body (which undergoes the process of birth, old age, disease and death), is full of misery:
mam upetya punar janma
duhkhalayam asasvatam
napnuvanti mahatmanah
samsiddhim paramam gatah
After attaining Me, the great souls, who are yogis in devotion, never return to this temporary world, which is full of miseries, because they have attained the highest perfection. (Srimad Bhagavad Gita As It Is, Chapter 8, verse 15)
Each living entities while in this body has to go through the 3 types of miseries (Adhyatmika, Adibhautika and Adidaivika)!
More explanations about the 3 kinds of miserable conditions in life by The Prabhupada Connection.
The symptom of the soul is consciousness. The soul accepts different bodies according to the performed karmas and desires. This accepting of another body occurs after death. The process, called reincarnation, continues since time immemorial.
Now one can think, this seems like a prison! Well, it is: Google prison vaniquote
Is there an escape from this prison?
Answer: YES THERE IS!!
This escape route is called Krishna Consciousness and it can only be achieved in the Human form of life!
Read Srila Prabhupada's unmodified books to find out why, how and when this escape route should be taken!!