Nico looks at him with sympathy. Here's his 'I won't tell you you're not smart moment.' He gets the sentiment; he really does, but sometimes.

Sometimes sacrifices need to be made. Especially when you didn't want to make them; he's already made that choice for the gods. His memories flash to when he found out Jason was at Camp Half-Blood and telling everyone about Camp Jupiter, and then finding an amnesiac Percy at Camp Jupiter.

"I'm glad it worked out for you," Nico said softly. "But sometimes, it's not going to. And you realize, sometimes, you just have to honor the sacrifice your friend is willing to make."