Answer:
The detail that helps shape the central idea of believing and trusting in yourself is:
Mr. Bixby asks, “Didn’t you know there was no bottom in that crossing?”
Step-by-step explanation:
In "A Cub Pilot", Samuel is initially confident in his abilities to navigate without Mr. Bixby. That is why he says he can do it with his eyes shut. However, Mr. Bixby asks him if he is sure he can really do it. From this point on, Samuel doubts himself. Even though he does know how to do it, he becomes unsure of his ability. However, that was just a test. Mr. Bixby wanted him to learn to believe in himself, to not doubt his own skills. That is why he asks, “Didn’t you know there was no bottom in that crossing?”