Stubborn vs Stupid

At what point does stubborn become stupid? When and how do you determine if it's time to throw in the towel or fight another day?

I don't consider myself brilliant though I'm no idiot. I can hold my own in most conversations (unless Son #1 is using mathgeekspeak then, yes, I'm pretty clueless). I have the ability to tell stories readers enjoy because some of those readers have written glowing reviews. Whenever I send out a new submission, I believe this is the one. This is good, it will sell, ...