I'm still learning 4 balls. It's coming together nicely, after a period of not being able to do it at all, and then a period of rapid progress.
An observation I've made from my own practice.
If you read about how to practice 4 balls, people say that you need to get really good with two in one hand, in both hands. There are many places on line where I have read someone saying something like "I got up to about 500 catches in each hand, before getting good at 4 balls. It really helped."
Why someone who has developed that much endurance still attempts to count catches is beyond me, but that's another issue.
What I've found out is that you don't need to be able to do 500 catches or even 100 catches of two in one hand. You need to be able to do 20 catches. Why only 20? Because it's not the endurance that counts, it's the frequency and ease with which you can repeat the event of getting 20 clean catches.
As I have read elsewhere on this fourm, it's what you can do *every time* that really matters with juggling, not what your once-in-a-lifetime personal best is.
People say that 4 balls is doing two in one hand simultaneously with both hands. It is to a point, but it's not really the same. Not when you have both hands going at the same time. Your mental focus and what you concentrate on and how the two parts fit together harmoniously makes it subtly different. But it's different enough that someone who has incredible endurance at two in one hand but had never tried 4 balls, won't instantly be great at it. When the two patterns collide or drift apart etc, you realise there is a lot more to it than you were led to believe.
Therefore, to anyone who is learning 4 balls, I would say that once you can **consistently** get 20 catches of two in one hand in either hand, you can definitely start trying to learn 4 balls.
It took me about 3 months to reach this "massive" epiphany. I was continually getting frustrated, because I couldn't get my record past about 50 catches with two in one hand, and my left hand lagged behind my right. More often than not I couldn't get more than about 15-20 catches with either hand. I thought I'd never be good enough to learn 4 balls.
Then one day I read something that made me think a little differently and everything changed. I stopped trying to push my endurance of two in one hand towards 1,000 catches (or whatever) and the feelings of frustration and inadequacy went away.
I told myself instead that I didn't need to get any more than a maximum of 20 catches. It worked. Within about a week I could **always** get 20 catches in my right hand, then switch over, and **always** get 20 catches in my left hand.
At no point did I push for 25 or 30 catches. I just switched back and forth from hand to hand, limiting myself to a maximum of 20. With that my 4 ball fountain progressed fast.
The only other change I made was consistently practice starting my runs of 4 balls with **either** hand, not always starting with my right.
What relevance does this long rambling post have?
When I get to 6 balls, I will be adopting the same philosophy. I will aim to get no more than 20 catches with three in one hand, rather than wasting loads of time beating myself up. That, and the only siteswap I will use to get 6 balls is 666600 with a hand clap underneath. From what I can tell, if you get that seriously solid, you are only a few hours away from nailing 6 balls.
It's all about specificity and motor learning. It really does bother me when you see people recommending that juggling 5 chainsaws blindfolded whilst riding a unicycle backwards down a wet skate ramp will really help someone with their Mills Mess. Give me a break.
I've also found that the best thing I can do when I'm struggling with a pattern is to not juggle at all for 2 or 3 days. When I come back to it, everything seems to much easier. It seems like the spaced learning effect, but with physical skills (http://en.wikipedia.org/wiki/Spacing_effect).