I was at a ceilidh the other week, which had attracted quite a few students who were bright, but hadn't done a lot of dancing before. After a few successful contras, the caller tried Fiddleheads and it, err, really didn't go well. I've been musing about why, and I came up with the following theory about folk dance move hardness.
Folk dance moves have (at least) four axis of hardness.
1) Simple to Complex. This is what people usually think of as 'hardness'. Walk in a circle is easier than walk in a figure eight.
2) Group to Solo. This is about two things, whether everyone else is doing the same thing as you, and whether there is some way to physically drag you through the thing. If four people dance round in a circle, that is easier than if the first person skips round the rest of the people who stand still, even though the physical move is the same for that person. Dancing is easier when there are people to copy and people to guide you.
3) Common to Rare. A do ci do and a mad robin are remarkably similar moves. But one happens all the time, and so people know what it is, and one is a rarer thing, so people aren't as immediately sure what to do.
4) Returning to Rearranging. Some things get you back to where you started. This is easier than having to be somewhere else, because if the (eg) reel goes completely wrong, you can get back to where you started and you are in the right place for the next bit. Some things progress you in fairely standard ways (eg move the 1s to below the 2s). Some things just Totally Rearrange the Set (eg tea kettles changing orientation, or turning four people in a square into four people standing in a diamond). This is harder than just getting back to where you started.
5) Short to Long. Things that start hard get easy when you do them for 16 bars, so half a ladies chain is harder than a full ladies chain not just because of the improvement in returning v's rearranging, but because you get longer before you have to worry about the next thing. (There's probably another thing about density of hardness, one hard move in a dance where everything else is circles and stars will fly more than 10 different hard moves linked together).
So you can now think about folk dance moves on these axes:
Circling - simple move, very group (everyone holds hands and does exactle the same thing), very common, completely returning, goes on for 16 steps usually - this is about as easy as it gets.
Circling three quarters - as above, except less common, and no longer returning, more rearranging, and just 8 steps, so harder.
Do si do - simple move, but a bit more solo (you're moving in the opposite direction to your partner, no-one is holding your hand or steering you, but you are mirroring what they are doing), very common, completely returning, not too rushed.
Reels - more complicated move, surprisingly solo (no-one leading you, or anyone you can directly copy), but fairly common, and returning, usually has quite a lot of time for it though.
Ladies' chain - more complicated move, quite balanced between group and solo (you are always holding someones hand, but not doing exactly the same as anyone else), fairly common, and returning.
Petronella - quite a complicated move (turning one way while moving the other), balanced between group and solo (you are doing exactly the same as everyone else, and can have a quick tug in the right direction from the circle, but you do your turn on your own), not that common in English ceilidh, and not immediately returning (until you do four), and quite quick.
So this is my theory about what went wrong with the start of Fiddleheads (1s cross over (passing right) and go left around one person into the middle of the set, lady facing down, man facing up, so you form a diamond, the first man with his original twos, but the first woman with the twos above) It's a fairly simple move - four steps across the set, turn left, come back to the middle of the set. But it's almost totally solo (if you're very leet and remember to look at other sets you can copy your mirror further up, but no-one else in your set is doing the same move as you), it's very rare (99% of the time if you cross with your partner you both turn together down or up the set, and you hardly ever stand in diamonds), it's ridiculously rearranging - half the people don't end up dancing with the same group of 4 they started with, you don't end up back in a longways set, you end up in diamonds, and it's pretty quick, you go straight into the petronellas without much time to catch your breath.
Of course, the real reason it didn't go very well was because the newest people turn up last, and are then dancing at the bottom of a set miles away from the caller (in quite a flat hall) with other new people. I don't know how you fix that.
I think this gives us a framing to think about which things will be hard for different groups. With complete newbies, the common / rare axis goes away completely, because everything is new (although over the course of an evening things that build on earlier dances help). With a mixed crowd of experienced and new people, you'll get through things that are very hard overall so long as they're a lot more 'group' and a lot less 'solo'.
Anyway, just rambling...