[It's a question that strikes in a way different that Ling must have intended. Because if he did sacrifice any chance of being with Katara... he could master the Avatar State. But that itself was a double-edged sword, since it was caring for Katara that made him want to do that, but if he saw her as any other person...]

Because she's been trapped by knowing everything about our future back home. And if I push too much, it... it can't work. I'll just be part of this thing that's trying to force her into someone she's not.