Human beings experiences greater sorrow, misery and pain than all other creatures. Sage of Kanchi answers to why this is happening.
Animals grow transversely. That is why they are called "tiryak" in Sanskrit. Man who grows upright ought to have, unlike beasts, a high ideal before him. He will then obtain more happiness than all other creatures. But what do we see in reality? Man experiences greater sorrow than all other creatures. Animals do not know so much desire, so much sorrow and so much humiliation, as do humans. More important, they are innocent of sin. It is we humans who keep sinning and suffering as a consequence.
In one sense it seems to me that Isvara has not endowed us with the same advantages that he has endowed animals with. We are not fitted with weapons of defense. If a cow feels threatened it has horns to defend itself. The tiger has its claws. We have neither horns nor claws. Sheep have hair to protect them from the cold of winter, so too other animals. But man is not similarly equipped. So he cannot repulse an attack; nor can he run fast like the horse, which has no horns but is fleet-footed. Against all these handicaps, man has the advantage of being more intelligent than all other creatures.
But, even with his superior intelligence, man suffers. All hardships stem from the fact of birth. How can one save oneself from being born again? But, then, what is the cause of our birth? The wrongs committed by us are the cause of our birth and we have taken this body of flesh and blood to suffer punishment for the same. Suppose a certain number of whiplashes are to be administered according to the law. If the body perishes after ten lashes, we take another birth to suffer the remaining strokes. The sins we commit in satisfying our desires are the cause of our being born again and again. If there is no "doing", there will be no birth also. Anger is responsible for much of the evil we do and desire is at the root of it. It is of the utmost importance that we banish desire from our hearts. But it is not possible to remain without any action after having cultivated so many attachments. If the attachments were done away with we would cease to sin.