Learning Haskell is not out of the question for most devs. The real question is whether they're willing to let go of a lot of their programming experience so as to admit a different style of programming.

It's more akin to studying than anything else. I've had evenings where I've been unable to proceed because I can't write one line. It's OK; it's part of learning. No one said it would be easy.

Beginner's mind is key.