Here, in the begigning, after the crash Brian brought himself to shore and has only been sitting in on spot, just waiting until the search planes came to find him. Then he realized that he wouldn't be saved so quickly. He would have to rely on what he saw in movies and in books in order to figure out what he needed to do to stay alive until he was rescued. He learned that he would have to push himself to his limits. He would have to become one with his new surroundingc.
Here, in the middle of the story, Brian is going through a hard and emotional time. He has been alone and is struggling to stay alive as he gets challege after challege thrown his way. However, getting through all thse challenges has changed him. He has a new perspective on the world and everything around him. He has a new gratitude for everything that he owns. Being able to survive has made him into a different boy from when he first got there in the crash.
Here, in the end, Brian is finally starting to really understand that in order to get through his problems, he would have to stay strong and work harder each time. He knows that he can't just give up. He does whatever he can to get through the situtatuions that are thrown his way, because if not, it could be his life on the line. He struggles to keep himself alive but still gives it his all.