The Blessing of Stability
It's mentioned in this chapter, and in the preceding chapter's epigraph, where the epigraph author notes that it is "rarely used." There's a simple, rational reason why you never see this one getting used in the book.
I added the Blessing of Stability after the fact.
You see, I realized that I needed at least one more Blessing to fit with what I'd built for Hemalurgy. I needed another mental power to complete the set of four. Two are the basic physical powers from Allomancy and Feruchemy: strength and fortitude from one, increased power of the senses in another. However, for Allomancy and Feruchemy, the mental powers deviate from one another. So I wanted the same thing to happen here. Hence the Blessing of Presence—which makes the mind more stable.
But after writing the book, I realized I needed a forth. The Blessing of Stability was born, and I wrote it in in a few places just to make token note of it. I like the concept for the power—that of making one emotionally stable—and am kind of glad I don't show anyone using it. I can show it off better in a later book.