There are 3 things which can affect the making of a drawing: skills, draw tools and will. The skills for making some great performance for making accurate shapes, the draw tools, even with the best skills and determination, the quality of tools can affect the appearance of the draw and the will for deciding if we want to make it to the end, partially or giving up the whole thing because it's scrapped. Also, some people makes good draws but they made one or several mistakes and they don't give a shit for fixing it.