What causes suffering?no_redirect=1

The explanation for pain and suffering is that Jivas live in duality where there is both pain and pleasure, both happiness and misery. You can't have only pleasure and no pain since this world is in a state of duality. Only in the non-dual state is there no such pairing.

Brahman is beyond vidya and avidya, knowledge and ignorance. It is beyond maya, the illusion of duality. The world consists of the illusory duality of knowledge and ignorance. It contains of knowledge and devotion, and also attachment to 'lust and greed'; righteousness and unrighteousness; good and evil. But Brahman is unattached to these. Good and evil apply to the jiva, the individual soul, as do righteousness and unrighteousness; but Brahman is not at all unaffected by them. One man may read the Bhagavata by the light of the lamp, and another may commit a forgery by that very light; but that lamp is unaffected. The sun sheds its light on the wicked as well as on the virtuous. You may then ask, 'How, then can one explain misery, and sin and unhappiness?' The answer is that these apply to the jiva. Brahman is unaffected by them. There is poison in a snake; but though others may die if bitten by it, the snake itself is not affected by the poison.