User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-170.235.245.55-20130515184452/@comment-3146930-20130520030214

This is the conversation in The Sea of Monsters I was talking about:

''"Where are your cabin mates?" I asked. "You were allowed to take two friends with you, weren't you?"''

"They didn't...I let them stay behind. To protect the camp."

"You mean even the people in your own cabin wouldn't help you?"

"Shut up, Prissy! I don't need them! Or you!"

As far as quest's go, three is the recommended number as it is sacred. Think about The Titan's Curse. 5 people started the quest (Zoe, Percy, Grover, Bianca, and Thalia), but only three made it back (Percy, Grover, and Thalia). In The Battle of the Labyrinth, the original team was Percy, Annabeth, Tyson, and Grover. However, Tyson and Grover leave to find Pan, dropping the team down to two. Then Percy and Annabeth get Rachel to help, forming a team of three again and finding the workshop.