Learning Ruby itself was a huge influence to me; hadn't considered that a language should be designed to make programmers "happy", as Matz said. "Confident Ruby" was one of several books that had this human-happiness focus. "Confident" is broken down into patterns, many of which can be found in books like Sandi Metz's POODR, but as a semi-experienced programmer, Grimm's way of writing really appealed to me.
Even the title of the book itself was revelatory to me. The idea that the functions and methods and conventions we create should be rooted in a "confident" mentality (such as the old adage of being promiscuous in what a function accepts, and strict in what it returns) really improved the way I designed code. Not just in terms of technical proficiency, but with less cognitive burden, which ultimately leads to the elegant simplicity we desire in our work.
FWIW, I almost never use Ruby today, having switched to Python for both teaching and development purposes. That doesn't mean that learning Ruby didn't influence me. For starters, it taught me the dangers of giving programmers too much syntactic freedom :).