In a good paint job there are many thing involved to make it look right. Any monkey can pull the trigger and squirt paint. Body work and prep are critical . If it ain't straight underneath the paint
it will look like crap, shinny crap, but still crap . While you can polish a turd, ( thank you myth busters) it is still a turd.
The Human brain is an amazing thing, the way it processes what it sees, and inputs it to the brain , The way that I understand it the eyes only pick up a certain number of things in a mental image and the mind fills in quite a bit of the picture. As a result a few small 'errors' in a car will not be picked up by the human brain, but the more 'errors' there are the more the mind will pick that up, once it reaches a certain level , or crosses a threshold, the part of the mind that does the filling in, says , " something isn't right". It isn't exclusive to cars, I learned this while I was in my last career , real estate .
The threshold is different to every single person. While I have trained my eyes and mind to have a very low error rate. by looking close and slow, using your eyes, as a secondary sense and using the skin of my finger tips as my primary sense.
We, ( 00 dub and I) well spend 16 man hrs , or more, doing this prep work on each of the sections before we shoot. The reason we do it in sections is more to do with not being overwhelmed , or overloaded with the scale of what we are working on, by breaking it down to a manageable level we are able to make a as close to perfect surface as we can.
All we are doing is eliminating the errors . you must be in the moment and in tune, if you rush it or push it, you will miss the devil because he is in the details.