Luck?

To me, luck took place about 70% while you are surviving. The rest of the 30% are knowledge that you learned,saw, or heard. Brian used his knowledge to build shelters, find food, and make weapons to protect himself. This is where luck came to place. If Brian didn't see the birds, he wouldn't find the berries for him to eat. He was lucky that he saw the birds eating those berries while he was searching for food. When the plane crashed, he was lucky that he survived from the crash. Not everyone can walk away not badly hurt from a crash. He was lucky that the place he crashed has food and water from him, or else he would die a lot earlier before anyone could find him. Like I said, survival is not all about luck, when he tried to make weapons for protection, that was when knowledge can to help out. If he never saw any videos, books, or if no one ever talked about or taught him about these things. He would not be able to make these weapons that he had made. So as the other things he made, the reason that Brian knows how to make them is because he was taught or he saw them.
Luck doesn't always help me. When I was in a tennis game, when all the pressure is crushing you. This is when luck doesn't help. All you can do is to use your knowledge and experience to fight back.