dreamed last night that somebody had smothered me with a wet rag … a certain person … well, I’ll tell you who: just imagine—Rogozhin!
I still don’t understand Rogozhin’s involvement with Ippollit btw <3
Actually, I do have an interpretation but it may be far-fetched: Ippolit and Rogozhin are both directly symbolically bound to Myshkin through their loves and in some other way. Rogozhin has been paralleled as Myshkin’s complete opposite since the very beginning — in the train, asking him if he was cold and letting him know about his inheritance of a large sum; in Part 2, when Myshkin was wandering around Petersburg feeling like ‘Rogozhin’s eyes’ were omnipresent; in Part 3 when Rogozhin showed up in the darkened park out of nowhere to talk about Nastasya. These two are bound not just as complete opposite, but in their love for Nastasya.
Ippolit is more like a foil. He and Myshkin have much in common, but Ippolit went in a completely different path from Myshkin. Myshkin went to one extreme — believing that paradise on earth is possible, and Ippolit to another — complete atheism and scorn against God. And these two are both in love with Aglaya.
I’m that way, Rogozhin ‘haunting’ Ippolit enough to warrant him to reach his ‘final conclusion’ (3.5), and now having a dream with a wet rag, not to mention even having a correspondence or association with Rogozhin, makes sends knowing that they are both comnected to the central character is some significant way — the central character who is about to break, in some thanks to them both tormenting him in some form throughout the novel.

