Those who hold themselves under the sway of ignorance, who serve the flesh and neglect the Atman or the real Self, are not able to perceive the effulgent and indestructible nature of their Soul; hence they fall into the realm where the Soul light does not shine.
The Isha Upanishad shows that the only hell is absence of knowledge. As long as man is overpowered by the darkness of ignorance, he is the slave of Nature and must accept whatever comes as the fruit of his thoughts and deeds.
When humans stray into the path of unreality, the Sages declare that he destroys himself; because he who clings to the perishable body and regards it as his true Self must experience death many times.
When a man performs actions clinging blindly to his lower desires, then his actions bind him to the plane of ignorance or the plane of birth and death; but when the same actions are performed with surrender to God, they purify and liberate him.