Allon Gay Bergeres "Come, happy shepherdesses", Guillaume Costeley (1530-1606).
It's a beautiful little Christmas carol -- but it's tough because it does things that modern music doesn't do, and it goes FAST. If you so much as pause to say to yourself, "Oh, (*&^*^%*^~!" you are instantly 2 measures behind and will NEVER catch up.
Not to mention that it's sung in archaic French . . . and I don't even speak modern French.
If people sang more, easy stuff like the NA wouldn't seem so hard to them. For heaven's sake, just sing along with the RADIO!
Often drunkenly and badly, but that's infinitely better than not at all. And the "Anacreontic Hymn" was probably mostly sung by drunks.