One limb fine,two ok, three hmmm,four aaarrrrrr!.
So why is four way co-ordination more difficult?.
easy it's "four" times as difficult?
Well no actually.
It's more like "twelve" times!
playing a single limb pattern,we pay full attention to the one limb.
When we add a limb attention is split between two,or
We usually hear the two as one new and separate interaction.
e.g. Swiss triplet.