Why does her heart refuse not to settle? 

"I fail you, and I will never be worthy of your wife."

Xia Sha's reason sounds absurd in Guan Xian's ear. He could not accept her rationale or that he could fathom what's going on in her mind right now. 

Guan Xian just wished that he could stop that brilliant analytical mind of Xia Sha from overthinking amidst struggle like this. 

"What I fail you, you fails me? We aren't in an exam! We are in a relationship. We are bound to make mistakes because we are only human. But that's come with the package. Right? We are supposed to make mistakes, forgive and learn from them in a relationship. Isn't it?" Guan Xian furrowed his eyebrow, sounds frustrated when Xia Sha exhales a heavy breath. 

"It's not like that. You won't understand," Xia Sha looked away, refusing to clear Guan Xian's confusion.