My first experience with functional programming was at university. I was a 20-year-old geek who was interested in Sci-Fi, reading, and programming; programming was the highlight of my academic life. Everything to do with C++, Java, MATLAB, and a few other programming languages that we used was fun for me. Unfortunately, I can't say the same thing about the disciplines around electrical engineering, circuits, or compiler theory. I just wanted to write code!
Based on my interests, functional programming should have been a very fun course for me. Our teacher was very passionate. We had to write code. But something went wrong—I didn't click with what the teacher was telling us. Why were lists so interesting? Why was the syntax so backward and full of parentheses? Why would I use these things when it was much simpler to write the same code in C++? I ended up trying to translate all the programming constructs I knew from BASIC and C++ into Lisp and OCaml. It completely missed the point of functional programming, but I passed the course and forgot about it for many years.
I imagine that many of you can relate to this story, and I have a possible reason for this. I now believe that my teacher, despite being extremely passionate, used the wrong approach. Today, I understand that functional programming has a certain elegance at its core, due to its strong relationship with mathematics. But that elegance requires a sense of insightful observation that I didn't have when I was 20, that is, a sense that I was lucky to build on after years of various experiences. It's obvious to me now that learning functional programming shouldn't be related to the ability of the reader to see this elegance.
So, what approach could we use instead? Thinking about the past me, that is, the geek who just wanted to write code, there's only one way to go—look at the common problems in code and explore how functional programming reduces or removes them entirely. Additionally, start from the beginning; you've already seen functional programming, you've already used some of the concepts and constructs, and you might have even found them very useful. Let's examine why.