The best that they can hope for, if they want to move ahead, is to go deeper into their soul's dark pool, where even footsteps disappear. After a certain point, there is no path to follow. Allums talks about the importance of heeding dreams, something Dante himself had done. From the very beginning, Dante distinguished between the true way and the false way. The journey was his first task.
Important journeys follow the soul's path, such that down becomes up.
To descend into your deepest thoughts is the true way. If you want to get to the light, you have to turn your back on it and go in the other direction. It's all reversed. That's a pretty shocking idea. Dante, in midlife, answers a divine call to write this poem.