I think functional programming in general is part of it, for sure. That said, my first success with functional programming was actually with Racket. Racket is

I think functional programming in general is part of it, for sure. That said, my first success with functional programming was actually with Racket. Racket is great for learning (in my opinion), but the "lessons" Racket had to offer weren't really solidified for me until I moved to Haskell. At that point, things really started to click. That could be due to any number of things, though. However, certain concepts (e.g., laziness, typeclasses) are more Haskell-specific (or at least are not common among all functional languages).