How we cite our quotes: (Chapter.Paragraph)
Quote #4
The gun didn't fire, but Brian had demonstrated, at least for an instant, that he was as daring as his older brother. (17.34)
Brian isn't quite as ambitious, and Fawcett recognizes that, which is why he chooses Jack over Brian. Just because Brian is daring, that doesn't mean he has the same goals as his father. Plus, there's a fine line between daring and recklessness, and we think Brian falls on the reckless side as a child.
Quote #5
Jack didn't hesitate. "I want to go with you," he said. (18.4)
We're not sure what Fawcett wants to do if he actually finds Z, but Jack appears to want fame. That's ambitious, too, if a different kind of ambition. Without reality TV, Jack thinks the ticket to fame is to find a lost Amazonian city. Hey, at least you had to do something to become famous back then.
Quote #6
"One learns little from a smooth life, but I do not like roping others into the difficulties which have dogged me so persistently… It is not that I want luxuries. I care little about such things—but I hate inactivity." (18.9)
Fawcett wants to achieve his goal so much that he gives up almost every life luxury on his quest. That shows us how determined he is. Finding Z is more important to him than anything else.