Had my friend T staying with me recently. He teaches in a different field than I do, but there are many cross overs in that his material includes physical skills, problem solving, controlling mental state, and using tools amongst other things.
Watching him teach, hanging out, talking, made me realize how much we take for granted, and by that I mean that we assume that we 'know' certain things when really we know only an approximation.
This approximation is usually good enough for day to day life, but falls short when skills become important or crucial, especially to one's survival. So why not be accurate all the time? Why be content with the approximation as a standard? Is it lack of incentive?
For instance, I paint for a living and can cut very straight lines with a paint brush without the use of tape. This requires knowing how much paint to hold in the tips of the brush - not too much, not too little - and how to place the brush on the surface without dripping or getting too close to the edge, it also requires a certain confidence and commitment that makes pulling the brush in a straight line in one pass possible - hesitate, twitch, or have your eyes wander off the line, and every uncertainty and correction will show.
Now most of the time there really is no need to be super accurate, if you get a little paint on the window glass you can clean it off, or fix a wavy line later with a bit of touch up, but there are certain times, where there is no margin for error, and you only have one chance at it. Perhaps you are painting up to some precious surface you cannot get any paint on, and now it really really matters whether or not you can make an accurate, straight line. You have one chance and a mistake may be too expensive an option to contemplate.
If you don't practice a high level of accuracy often, this added stress makes it twice as hard because now not only are you less practiced, you also know it, which adds to the possibility that you will screw up through hesitation or lack of smooth control by being too tense.
So I always cut straight lines, as smooth and as accurately as possible. I practice when it does not matter, when there is no performance anxiety, each and every time, and try to ingrain the mental focus, the relaxed state, the hand eye coordination needed to do the thing I need to do. Then when it really does matter .... I can access the focus and the state as familiar, without wigging out on the fact that this time it's 'for real' and now the stakes are much higher.
It's amazing how your mind effects your movement, especially the fine motor skills, (not exactly news to fencers or gun folks), but I wonder if every time you did anything - catching, throwing, aiming, cutting, parking - you did them as precisely, smoothly, and accurately as possible, whether the efficiency would cross over to all motor skills, and make doing things that required accuracy under stress that much easier?
It's the state you have to access, the process, what it feels like to do do the thing right that seems to be the key. If you can do that, doing the thing itself becomes easy, regardless of external or internal interference.