Ok, so you understood flatmap and therefore monads in 2 minutes. Now you need something that needs nested monads. That's where major complexity suddenly appears

Ok, so you understood flatmap and therefore monads in 2 minutes. Now you need something that needs nested monads. That's where major complexity suddenly appears - your code is no longer simple and is full of artificial constructs like transformers just to do simple things. Moreover, anyone who reads your code must know all language constructs you are using or they are lost and can't fix any issue in your code.