With something like this I will carve the form over and over again, smoothing it back and doing it again. sometimes I will get a section right and be able to leave it, but mostly the interrelations of the lines mean I frequently will need to do the entire figure over. The key frustration of this is that I might have a line that is good, but I will seek more from it and will erase it in the hopes that the next one will be perfect.