THINKING OUTSIDE THE BOX

Plato and Sartre both write about the limitations of the mind.  Plato uses the "Allegory of the Cave" to represent how we can bind our own minds to shackles by not gaining the knowledge the world has to offer.  If you live in the cave, you have your own reality and perspective which doesn't represent an accurate representation of the world.  Some people could consider this hell.  Some people could also consider No Exit hell too, which represents how people can be the greatest torturers of them all.
These stories also represent how knowledge may be powerful but it also can hurt.Throughout No Exit, the characters look down at Earth and see how their "loved ones" have moved on or what has happened since their death, most of which hurts each of them in some way.  Plato writes that once you have left the cave and gained knowledge about the world, going back to the cave would hurt because you must lose all your sense of surroundings and live with ignorance.
Both use imagery, extended metaphors, and irony to emphasize their points.