I really can’t describe it. The project just seems to get all jumbled up. This happens to me a lot when I’m transforming things. As an example, I was trying to follow exactly what was happening when modeling the brackets prior to applying the mirror modifier, but when I do it, the bracket ends up too short, too tall, too thick, etc.
Another reason I’m having trouble following along is that things are happening much to quickly. Sometimes a selection is made, and I can’t determine what was done to get the same selection. For example, in the first video, when the top boards are selected for extrusion in the previous video, it seems to happen all at once, but it goes to fast for me to see the keystroke or mouse move that made it happen. I kept getting it wrong. On my tenth time through that video, I discovered (by trial and error) that it was l (for selecting an island).
I have a problem with spatial relations (in aptitude tests, I consistently rank in the 5th percentile). Computers have helped me compensate in many areas in which I have trouble due to neurological defect. This includes visualizing objects. Unfortunately, the software I used to use for this has been defunct for a long time, and since current software is “better” for actual artists, nothing really works like that old system. (The advantage for me was the translation between wire frame modeling and source code.) One thing that helps me with blender is having numbers to apply to the operations. I can then pause and try minor adjustments, and I can get a better idea of how the process works.