I have been very happily using only one blue-black ink for years (Rohrer & Klingner Salix), but have also been coveting one other (Pelikan Edelstein Tanzanite) for several years.
At Christmas I decided to treat myself to a bottle of the Tanzanite, in order to finally be rid of the nagging craving.
Within a month of doing so, I have found this thread, and now I find that I am coveting Sou Boku
I suppose it simply must be the case that the number of inks that one has in one’s possession is doomed to always be ‘n-1’, where ‘n’ is the number with which one would feel satisfied/sated.
"Possession is nothing. But absence has breath"
(You must get a bottle of Sou Boku though)