To understand the mystery of pain you must understand the mystery of the pairs of opposites.

While man lives in this world of illusion (mâya) he is subject to its laws and cannot experience Heaven unless he also knows hell ; he cannot have life without death, nor joy without pain, he is living the separated life in the shadow world, if he could turn from this unreality to the real, for him pain would cease, he would have " crossed over the illusion " and discovered the secret of the pairs of opposites ; while they are divided they delude man, but when they can be united or balanced, they reveal the innermost mystery of being.

" The Eternal is Incorruptible and Balanced,
the knower of the Eternal neither rejoices on obtaining what is pleasant
nor sorroweth on obtaining what is unpleasant."

But man has freewill and the experiences of every man are according to his beliefs.

«The faith of each is shaped to his own nature, a man consists of his faith.
That which his faith is he is even that. "

Bhagavad-Gita 

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