From Fallen London Wiki

as far as i can tell, this is framed as an entirely in-character statement...? this is a thing the steward is actually saying, diegetically. which means that all the things involved aren't gameplay abstractions: in the Neath, by some treachery, a person's nightmares *are* just a number, a quality level with change points attached, which can be manipulated through performing certain actions, and which can thus be aligned with another number. there is a tangible and *real* (insofar as anything in the Hurlers is real) manner in which all these things are, even from the perspectives of the characters involved, *just numbers*.

i suppose this shouldn't be strange. the treachery of maps is why sunless sea's map randomization is diegetic. the treachery of clocks is why performing identical grinds over and over is diegetic. maybe one of the Three Beyond is the treachery that governs how the world exists as a quality-based narrative, and hence how everything that exists and doesn't exist is fundamentally quantitative in nature. the Treachery of the Nexus, if you will.