Ask HN: How do I develop polyglot thinking?

I am self taught for the most part when it comes to programming. The first thing I learned to write in C++ was a for loop. for (int i = 0; i <10; i++) { ... }. That's imperative. Now I write SQL for a living and still find myself not thinking in a very relational way. I have desires to learn what I can from the functional languages but have a hard time wrapping my head around the concepts to gain anything of value from it. My question: how do I enhance the way I think to be able to think in different domains and become a better engineer?