For an example of what can go wrong:

http://straightrazorpalace.com/honin...chips-why.html

And an example of "geometry problems" caused by bad grinding during manufacture:

http://straightrazorpalace.com/honin...r-trouble.html

I'm not experienced enough to distinguish between "too hard to be worthwhile" and "impossible". But I can tell you there's a big difference in "honeability" between a good razor (which includes almost all the vintage razors I've sharpened) and the bad ones.

Charles

PS: I sympathize with your wish to know why the bad razors are bad, and the good ones, good. I started out thinking that way myself. I don't care much, anymore. If a razor won't hold a good edge -- as proven by the hones and my face -- why bother with a Rockwell hardness test?