I always tell my students to embrace their "mistakes" when they are making any sort of art. People, and especially children, get a bit frustrated when something that they are working on goes awry and a lot of the time I feel as though this sadness or anger over a perceived problem may actually be missing the point as far as art is concerned. Some of the greatest artists of all time actually ended up turning their mistakes into fame and a new style of art that the art world has never even thought of.
So the other day when a student messed up really early on in a watercolor session I observed as he was trying actually to destroy the entire work after going outside of the lines, but then I told him, and I wasn't joking, that it is actually extremely creative and that I preferred it the way that his mistake made it look.
The student had been attempting to replicate a picture of an old car and the penciling and the ink work actually went very well. I was impressed with his precision. However, when it came time to fill it in with color he made a mis-stroke and the color scheme was all of a sudden out of whack and not capable of looking like the picture in question anymore.
The student, because he was angry, was attempting to ruin his own piece by painting intentionally out of the lines and this had him on the verge of tears because he had worked so hard on the outline. When I came along and said genuinely, "wow buddy, that is really inventive, I like it!" he thought I was joking at first but when he saw that I was really being sincere a smile lit up on his face. At that point he started trying to make his color scheme something that actually could represent the real world in a sort of abstract way.
This particular student is very exacting in his work and gets easily angry whenever something goes even slightly wrong but in the end, I feel as though the end result is much more captivating that if he had finished the piece while staying completely in the lines. In a way I felt as though the picture would have been quite boring if he had stayed in the lines and I personally feel that 1-1 replicas of photographs actually are quite boring. We have cameras for that and we don't need it anymore.
So if you start to make a mistake on something you are working on, perhaps it might not be a terrible idea to take a step back and wonder how can I make this artistic and unique. I always say that you never know, what you consider to be a mistake could be something that others, like me, consider to be very unique and interesting. I know that if I was in a gallery and there were two types of pictures, one that was a realistic replica of the real world and one that was very abstract, strange, and thought-provoking, that I would prefer the "weird" one.
There is no one way to do art, and if you make mistakes, perhaps you should look at them as attributes instead.