1) Poor bell control, as a result of having very limited bell control experience
2) inability to understand how to achieve bell going more quickly and more slowly - not as a matter of theory, but how the bell is physically moved to achieve that.
3) Because the feel and rhythm side has never been developed, the focus is follow x follow y, making ringing a visually dominated activity. Humanly that always seems easiest, but for musical performance, learning the feel of what you are doing (how it feels to do something) is the primary skill to learn.
4) use of apparently simple, but actually difficult methods for initial training, and focus on do x and next time you will do y, rather than you do x because y happened, which can make it simpler. Stedman is a better learning method than Grandsire doubles - get to do right and wrong work, and something is happening all the time. Also helps, initially, that the work is not moving the bell through the full range of front to back, so if mistakes are made it is easier and quicker to get back into place.
5) Learn ways of ringing that are not the way that the best ringers ring.
(c) Richard Johnston, 2014