Recursion is harder than iteration. Immutability is harder than mutability. Callbacks, dependancy injection, and implicit loops are hard to wrap your head around.

Oop is just a strut with functions and a fancy dress. It's not really a new way to think.

I trained many, many, many people in small groups in programming. The functional concepts are always the hard ones to explain.

And as a dev, even when i deeply understand the benefits of immutability, i find it often being a huge constraint for the most mundane tasks.

Most programmers make simple programs. They don't need complex tools.