You pointed it out yourself and others have confirmed it - practice is needed. But practice for what? If you can manage proper form in practice than surely you have developed the skill.
As Star pointed it out, it is the state of the mind. In other words, confidence in your ability to execute all required strokes properly and with control. The way to develop that is with 'mindful' practice i.e. you decide what you are going to execute and then do it mindfully - without hurrying through the stroke and hoping it will fall in the right place. This is developing muscle control as opposed to muscle memory.
I believe muscle memory to be a Calligrapher's enemy (I know I'm going to get flak for this but hear me out first :-)
Muscle memory is very much susceptible to degradation when the conscious mind starts to engage. Have you noticed your handwriting degrade when writing something important or something you want to be really good? The reason is that muscle memory resides at a sub-conscious level where we learn to execute certain patterns without thinking. It is very powerful as one can train oneself to do amazing things with absolute precision (e.g. hitting a baseball accurately at over 100 mph). However, the problem is that as soon as the conscious part of the brain begins to engage (e.g. stressful situations in close matches), our ability to execute with muscle memory diminishes. As our conscious part of the brain isn't as well trained, the results suffer. (I realize there is more to the functioning of the brain than this over simplified explanation but this should suffice to illustrate my point.)
So - all this is to say that we just need to train the part of the brain we will be using in situations when we need it to perform best. One technique I learned from my teacher was to do my exercises in groups of 5, and then stop and analyse the form. Place a tick mark on the best ones and then try to replicate the best one another 5 times. Repeat until you can consistently get 4 out 5 to be perfect. This engages the conscious part of the brain and also keeps boredom at bay as you are always busy doing something. Practice sessions should not be longer than 15-20 minutes.
The pre-requisite for this is that you should know proper form and should be able to analyse your work accordingly. This is the 'study' part the masters talked about.
It doesn't work so well for sports but fortunately it does for Calligraphy :-)
Please note that there may be other ways to achieve the level of control needed. I am just sharing what has worked well for me and what I believe to be the reason for it.
Happy practising,
Salman
