Not the अज्ञान/ ignorance but the superimposition/ अध्यास is the cause of miseries.

There were two boys ( friends).
boy1 was used to hear the stories of the ghosts from elders and friends. He was having many ideas about the ghosts like they are white and tall, fierce, etc.
Boy2 never heard anything about ghosts.

One day, at late evening, both the boys were returning home from the playground at outskirts of the village.

As darkness increased, both started walking fast to reach early at their homes.
Suddenly the boy1, who was believer of the ghost,  stopped and started shouting like anything.  He was trembling with fear and sweating too.
Boy2 was surprised to see his friend in such a miserable state. Holding his trembling hands, boy2 asked;  “Why are you shouting?”
The boy1 pointed towards something and said- ” There is the ghost….it will eat us both.” and started shouting again.

The boy2 goes towards pointed direction. What he sees there, a  white goat  eating the leaves of the higher branches of a tree, standing upon his hind limbs.

The boy2 consoles boy1 making him clear that there is not a ghost but a white goat.
After knowing the fact, boy1 get relaxed and starts laughing. Both returns home happily.

While walking, at first, boy2 didn’t see the goat. That means he was ignorant about the goat. So he was walking at ease without fear. ( Ignorance is bliss- its negative).

But when his friend showed him the ghost with fear, he straightaway went and confirmed that it was a goat. He had no doubt or confusion , so no error of superimposing idea of anything else occurred.  ( Complete knowledge is Bliss..it is absolute. )

Boy1 saw a goat…but not as a goat….he has seen something white and tall. Because of insufficient light, he was not sure about that something. Errors occur whenever you are in doubt or confusion. He was in a state of  partial knowledge and Partial ignorance. So he has superimposed an idea of the ghost upon the goat.
(characteristics of the ghost he used to hear that it is a white and tall matched with the few characteristics of a goat – white and tall. And as not all the characteristics of the goat were seen clearly because of the insufficient light, he assumes goat as a ghost.)
Thus the cause of his sufferings( shouting with fear) was the superimposition/अध्यास. 

Had he been totally unaware of the goat( like boy2), he wouldn’t have shouted with fear.

In deep sleep/sushupti, jiva is in blissfull state, free from anxiety and fear. Because there is the complete darkness of the ignorance. (In complete darkness, rope is not seen so no question of projecting a snake upon it.)

In waking and dream state, a jiva who is ignorant  because of incomplete knowledge, considering himself as limited, suffers like anything. He superimposes the qualities of the limited body mind complex upon own Self/Atman which is limitless (Nitya, Shuddha, Buddha, Mukta) and suffers.

But in Awakened state, one has complete knowledge.  There is no confusion or doubt regarding own nature. Those who are awakened, see the things as they are….just as the manifestation of the Brahman. There is neither non-apprehension nor mis-apprehension….the state of Absolute Bliss.
    Hari Om!