Good evening Zito, I might have spotted something that hinders incremental progress during single backbone drawing. This is a mistake that I made and took quite a while realize.
It appears you are using a drawing program, maybe procreate or something similar. This seems like a good idea but here is the problem. You draw a single line towards becoming a backbone, you try and do this in a single stroke… there comes a point where you are displeased and then implore the dreaded eraser tool. Because you are in that electronic program all traces of that line are gone forever… there is no reference for making progress, the next line has no more chance of being perfect than the first. This can repeated a thousand times and unless a miracle occurs all your left with is a blank drawing document.
So a piece of paper and a pencil is the simplest and greatest tool for learning. Now replay the previous events only draw lightly in pencil and get as far as you can before you notice a flat spot, off angle, drastic curve, anything. Say its a flat spot add a little to the edge, lightly erase some don't make it perfect just get it headed in the desired direction. Continue your backbone towards the center make small adjustments, add, take away, but drawing lightly you can build off of each line and you can still see where you were and how much closer to desirable you are getting.
Give it a shot, couldn’t hurt and have a great day. BB
