I've seen people master it quickly, writing their own behaviours etc..

I learned it on the tube to and from work in a relatively short space of time, writing a comet server for streaming updates to browsers with a colleague. After the initial hump it was easy and fun. I don't claim to be a genius programmer, just an interested dabbler.

To be fair though, the more average developer does struggle with it, and that was a reason my company didn't take it up widely.

Took me a week to be comfortable with it, but would take at least 2 years for me to grok the performance implications of each construct.

Erlang is the first functional language I've written, and I found it very easy to get going with. The syntax takes a bit of getting used to, but it's a compact language with not too many constructs to learn. I bought the Erlang and OTP in Action book to get my head around the OTP system, but the rest was fairly approachable.

Well, "Mastery" is a standard that I think, by definition, few achieve.

But competence in erlang is certainly achievable in a couple of months.

In my example, I started having never once written anything in a functional language. I started by reading Armstrongs book with pragmatic programmers. After a couple of months I could write anything I wanted to in erlang, without too much trouble, and much more importantly:

I was in love with erlang

The idea of writing something in erlang was very exciting and pleasurable to do.

I think that's quite an accomplishment for a language with such a different syntax and with me only putting a couple months into it.

Now, obviously, I won't say I'd mastered it. But prior to that I had the fear of the unknown when it came to functional languages, and a distinct repulsion at erlangs syntax. The only reason I learned it was that I believed it to be the only language that had done concurrency right.

And I had a project to write in it that required concurrency. That might be a big help. I imagine it is hard to learn any language if you don't have a goal that it is well positioned to achieve to work towards while learning.

I suspect people who think erlang is hard to learn, haven't spent any time learning erlang. But in truth, no language, except the very first one, was hard for me to learn.