“There's parts of me I don't understand, he said, and shrugged.”

“A student once interrupted him and said, "I just don't understand." He responded, "Why should you have the advantage over me?"”

“… You're omniscient, right?"
"For the most part, yes."
"Then you have to tell me this ‘cause I have to know. What's at the end of everything?"
He shrugged. "That's easy enough."
"Then tell me."
"The letter G.”

“It ain't the parts of the Bible that I can't understand that bother me, it's the parts that I do understand.”

“She pulled away. "That doesn't make any sense."
"Neither does this," he said, "but I don't care. I'm sick of trying to pretend I can live without you. Don't you understand that? Can't you see it's killing me?”

“Ah," said the magus, understanding at once. "I see that he means to be prepared if he meets him again."
"Surely that's unlikely," said Sounis.
"I don't think unlikely means to him what it does to the rest of us," said the magus.”

“I guess I don't really understand you yet,' I said. 'I'm not all that smart. It takes me a while to understand things. But if I do have time, I will come to understand you -- better than anyone else in the world ever can.”

“I don't understand you. You don't understand me. What else do we have in common?”

“I'm sorry," he says. "I don't usually like people. So when I do, part of me is really amused and the other part refuses to believe it's happening.”

“You dinna need to understand me, Sassenach," he said quietly. "So long as you love me.”