I found writing in Lisp was liberating, as everything can be reused into a bigger program. And Lisp is a functional programming language. It is also a programm

I found writing in Lisp was liberating, as everything can be reused into a bigger program. And Lisp is a functional programming language. It is also a programmable programming language, so you can even extend its syntax. I am interested in your struggle. I want to know what is really difficult about functional programming for a learner.