It’s mostly a matter of practice. I think that many people’s experience of functional programming is a (potentially poorly-taught) university course, during which there is not really enough time to really become comfortable with functional programming. Maybe it’s true that the learning curve is a bit (a lot?) steeper, though. But once you are comfortable with it, it’s not significantly more difficult than writing code in Java or Python. I also think that it’s worth learning even just for the sake of becoming a better programmer. It teaches you to think in a different way, which also translates to programming in imperative languages.