The narrator possesses an uncanny perspicacity, which he uses to identify individuals that pass by the window of the cafe in which he is sitting; from a person's "dress, air, gait, visage, and expression of countenance" (Poe 507) he knows that person's profession.
The man of the crowd is an oddity because the narrator cannot decipher his background. After pursuing the man through the streets of London, he realizes "[i]t will be in vain to follow; for [he] shall learn no more of [the man of the crowd], nor of his deeds" (Poe 515). The narrator acknowledges the futility of endeavoring to read the man.
Poe suggests that there is a limit to human understanding, or that humans are drawn to the occult (after all, the man of the crowd is described as a fiend).
-