What mistake did Brian make in the use of his hatchet? Why might this have been a costly error? But some good came out of it because Brian realized a way to make a fire. How did he get his idea?

Brian make a mistake when he threw his hatchet at a porcupine. This might have been a costly mistake because he made the porcupine angry. Brian did, however, learn that the hatchet created sparks when it hit the wall, giving the knowledge to make fire.

Brian also dropped the hatchet in the water while attempting to cut into the aluminum on the plane. This would have been a devastating loss.