I'll use the "fear is the mind killer" [1] quote when I'm upset or anxious quite often. I really should add this one to my arsenal as well. I've never thought of Dune as a self-help book but I might now. Weirdly enough I'm also currently re-reading it, after watching the miniseries due to quarantine, and I'll try to find more things like this during my reading.

[1] “I must not fear. Fear is the mind-killer. Fear is the little-death that brings total obliteration. I will face my fear. I will permit it to pass over me and through me. And when it has gone past I will turn the inner eye to see its path. Where the fear has gone there will be nothing. Only I will remain.”