The six line epigraph from Dante's Inferno translates as:
If I thought that my reply were given to anyone who might return to the world, this flame would stand forever still; but since never from this deep place has anyone returned alive, if what I hear is true, without fear of infamy I answer thee.
The lines are spoken by Guido da Montefeltro, a double-dealing monk consigned to hell for his fraudulent behavior. The shade of Guido wrongly assumes that Dante is also dead and that he can confess his darkest secrets to the poet. He thinks he is safe because he thinks that Dante will not be returning to the world above.
Prufrock himself is trapped in a kind of hell, a private hell of impotence, boredom, and social anxiety that permanently separates him from the world around him. But unlike Dante, Prufrock is not about to return from hell anytime soon. He spends so much time analyzing—some might say overanalyzing—everything that he can never truly escape the hellish confines of his mind. He confesses all to himself just as Guido confesses all to Dante. However, there is no sense that any of these innermost anxieties and secrets will ever see the light of day or that they will ever be revealed to those who pass by him in his daily life like ships in the night. Prufrock, no less than Guido, is a shade in a world of shades. But unlike Guido, he is incapable of reaching out to his fellow shades and showing them something of himself.