Leiningen's motto is "The human brain needs only to become fully aware of its power to conquer even the elements" (p.81). By believing this motto, Leiningen feels he can overcome anything. On one level, this is true, as rational thought coupled with decisive action can lead to victory. Leiningen is able to control his thoughts, and therefore, he is also able to control his panic in this situation. However, he is also overconfident.
Therefore, his weakness is pride which relates back to his motto. By believing in the above motto and convincing himself he can overcome "the elements" even as the ants approach, he elevates himself to a godlike status that no human can achieve.This raises a very important question: is man the master of his fate? Ironically, in considering his motto, it is not his brain but his courage and physical strength that defeats the ants.