Brian struggles for food sources. He realizes that catching fish in the L Shaped Lake could help him with this. His original attempt was to make a spear and use it to catch the fish. This was a good idea, but failed because of the refraction of life and the fact that its single tip proved to allow fish to escape. In order for Brian to be more successful, he aimed his speak taking the bending of light into account and then also created a double tipped spear. This allowed him to be more precise with his aim and catch more fish for a plentiful food source. This instance proves that Brian learned the element of persistence and mental toughness in that there is little fear of failure. He understands that there is little other choice than to fight through these setbacks and focus on what he needs in order to survive.
The above answer before mine is a perfect description of how Brian was able to perservere and continue improving on his previous failures. With the example with the spear, Brian initially struggled and could not catch any fish to eat. However, after a few adjustments, namely the double edged spear and using the sunlight to his advantage, he was able to conquer his previous setback and catch a fish. As a reader, it was a very exciting moment in the book when Brian first found success.