What determines a "bad normal"?

Eternal

L69: Deviant Member
Jul 8, 2009
69
10
I found and fixed the problem (which was an "invalid shape") But I was wondering what determines if a shape is invalid or what a "bad" normal is? The object I made looked fine to me as far as I could tell but the program didn't seem to agree with me.
 

A Boojum Snark

Toraipoddodezain Mazahabado
aa
Nov 2, 2007
4,775
7,670
Invalid solids are when the verticies of a face are not coplanar. Meaning the face "bends" rather than being flat.
A bad normal results from the texture coordinates/axis being improper for the face. In your case, probably because the face was invalid.