To them, I would suggest that they remember back to when they learned their first imperative language like Java or C. For me, that was really difficult to wrap my mind around at the time, but now those languages are second nature to me. I kind of suspect that if everyone were exposed to a functional language first, there would be a lot fewer people who think they are extremely hard to learn.

I fondly remember being confused by “return” for weeks (granted, I was 9). What are you returning? And to where? And why was it only one thing? And where did it go when it got there?

It’s easy to forget how hard something was to learn once you already know it.

I remember when I started with Java at University.

Like, "hello, what is a method? What the hell is a class? Come on, stop kidding me, objects have methods???? How do I call them? Wait, how do I _write_ a method?"

What I kept bouncing off of was all the stupid as shit "sally sends a BUY message to Tommy's bagel shop" crap. I just needed about two to four pages worth of text & diagrams demonstrating how objects and structs are pretty much the same thing, and what the OO sugar inheritance and keywords and dynamic dispatch and such do under the hood, which ain't that complicated. Every single book I picked up (back in the '90s, when if you didn't know someone to personally recommend a book it was much harder to figure out which ones were decent and which sucked) wanted to use those awful, cutesy analogies to introduce OO and they just confused the hell out of me, and convinced me something dead-simple was hard.

There are many reasons Haskell is difficult to learn, and the functional programming aspects are only part of it. I'd venture a guess that it's vastly easier to go from say, python to clojure, than from python to haskell. Even neglecting clojure's impure escape hatches.

If you are learning something new and it isn't hard to learn then you are not learning anything truly new. Just variations/flavours of what you already know. If it is really hard then you are truly learning something new. No pain no gain.