When I first heard this quote from Margaret Kilgallen it was an eye opener. A great example is in our design work,calligraphy,lettering we focused so much on getting everything crisp and clean. Not to say having clean and crisp design/lettering,calligraphy work is bad. More so that you can try and try to get your lines straight but it will never be straight.
Therefore that is where the beauty is. If you look at something that is hand done it captures a different essence to it. The feeling of not being done by a machine lacks certain aesthetics. Lets take hmm a Renaissance painting and compare it to a digital painting. The painting from the Renaissance will evoke more feeling of human like quality to the piece.
While the digital painting will have a mechanical feel to it. But this is could be up to debate for many people. I just want you to realize that the importance of having a human aspect to your work will allow you to invest yourself even more into it. Because if you look at someones lettering or calligraphy really close you can see the line waver.
Maybe from afar it looks amazingly beautiful. When close up you notice the flaws better. This involves training your eyes to be able to spot certain things. Another thing is with other aspects of lettering,calligraphy and graphic design.