In every task, the subconscious and conscious mind have specific roles to play, and a confusion of these roles can lead to less-than-optimal results.
In ideal piano playing--where there is effortless flow-- the simplest way I can state it is this: the subconscious mind sends information up, the conscious mind "OK's" it. In other words, the conscious mind simply monitors, but does not judge or ask questions. (Is this a drastic simplification? Yes. But it does the trick.)
One of the distinctive mental features of performing under stress is that the conscious mind tends to kick into overdrive. It asks questions rapidly, tries to take over the playing process, and generally raises a big fuss. Unfortunately, the conscious mind has a very narrow bandwidth, and is actually unable to handle the incredible amount of information and physical tasks required in the playing of the piano.
Pianists usually take one of two approaches to this problem (I suggest both). First, they train themselves to focus on something other than the actual playing of the piece. Usually they focus on the sound they are creating (instead of, say, the hitting of particular notes). With training, this is a great technique. Of course the problem is that any lag in focus and the conscious mind jumps right back in to trouble-maker mode.
The second method is to train the conscious mind to be aware of every single aspect of playing before performing. This method subsumes techniques such as mental practice, ghosting practice, analyzing, knowing the piece in sections, etc. The idea here is to allow the conscious mind to be active in the playing process, but so thoroughly prepared that it isn't overwhelmed by hyper-activation and can, in fact, relax. (The analogy might be something like taking a test on material you know inside out.) Ironically, this conscious preparation allows the conscious mind the resume its role as (intelligent) monitor.
The next logical question of course is: OK but how do you know when the subconscious and conscious mind have been trained appropriately? After all, the big problem is that people play just fine in their living rooms, but have so much trouble in lessons and performances. How can they prepare for this correct mental functioning? And to that question I say: wait for part two.
To be continued . . .

If you are interested in other instruments using keyboard similar to the piano lets say accordion this is the right blog for you http://accordionexpert.blogspot.com/
Posted by: Dache | February 24, 2013 at 02:28 PM
Great article I am looking forward to part 2. I know when I am well rehearsed I can play much more easily and the performance is more musical.
Posted by: Blair | February 25, 2013 at 10:52 AM
Great article! Looking forward to the second part!
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Posted by: Gabriel | March 20, 2013 at 05:30 AM
Really interesting point of view regarding the creative subconscious mind we all posses and find it hard to tune into it.
Posted by: Michael | April 01, 2013 at 01:32 AM
hmmm....this was a very interesting post indeed. Parallel to the 'thinking' self and the 'observing' self that I've been reading a lot about lately. Part II will be a good read I'm sure...
Posted by: DMG | April 03, 2013 at 11:51 PM
Very interesting..waiting for Part 2
Posted by: Alice | April 28, 2013 at 07:13 AM
Excellent advice. Personally, I don't know whether I lose focus or not. But when I play alone I play well. Almost every time I play in front of others, I end up making mistakes. I guess I get nervous. Hopefully, the advice in part 2 will be helpful.
Posted by: Arthur | May 16, 2013 at 02:13 PM
Great article. It takes years and years to get into the mindset from my personal experience. The first 2 years of learning to play a piano is finding the right key, feel, etc.....This is the next level, which some may or may not reach. Nice post.
Posted by: Bill Boggs | May 18, 2013 at 09:56 PM