I can really only speak from my personal experience here. I learned Clojure on my own time in college, and it took some time for me to understand how to deal with things like immutability, laziness, and pure functions. After I did finally 'get' it, I was unable to convince any of my classmates that the initial effort was worth it. I love the language and its opinions, but JavaScript (another language I learned on my own time) was probably 10x easier.
"I learned Clojure on my own time in college, and it took some time for me to understand how to deal with things like immutability, laziness, and pure functions."
I suspect much of that time was spent "unlearning" habits from procedural languages.
I know Carnegie Mellon now teaches functional programming as the introductory course, and only introduces advanced topics like "mutability" later. I think that sequence makes it easier for beginners to reason about what their program is going to do and experience less frustration.
