Plato and JeanPaul Sartre both wrote extended metaphors about...well essentially hell. Plato wrote is his "Allegory of the Cave" that ignorance is bliss but in the overall scheme of things ignorance becomes hell. Sartre wrote in his "No Exit" that simply "Hell is other people."
Plato's thinking that the choice to give up the pursuit of knowledge and stick with ignorance is easy. This choice leads you to stay in ignorance for the rest of your life, hell if you will, since it is all you know and care to know. Plato used metaphors, symbolism, and figurative language to describe his allegory and convey his message.
Sartre, on the other hand, was a little more direct with his theme. "Hell is other people." Sartre straight up told us what the message was. He also uses some symbolism and figurative language much like Plato but in the end he left nothing to chance in leaving interpreting the theme to the audience, might as well just tell them incase.