For me it was the part about typing JSON. I work at a company with a Common Lisp back-end and Let Me Tell You. Trying to enforce the JSON structure it generates using any kind of front-end JS types, so that nil-punning doesn't crash the UI every other day, is an exercise in attrition. Unfortunately JS is not Clojure and so can't as elegantly digest inconsistent data, but I certainly have learned to appreciate the appeal of that philosophy.
That observation on `Maybe` really hit home in a big way. Not at first. Eventually. I used to think that banning null and using `Maybe` instead was the best idea ever. I still love the basic idea, and wish I could always work that way. . . but nowadays I'm so frequently working in the limit case, where everying is either optional, or used to be optional, or will be optional in the future, or is officially required but somebody didn't get the memo. And it's like in some Zen parable where the student keeps getting hit with a stick until they're enlightened. Bruised, bloodied, and enlightened. You either have it or you don't. む.