What defines rational and irrational thought and behavior varies across cultures and generations. It all depends on one's perspective; however, a commonly accepted definition of irrational behavior seems to be behavior that lacks sound judgment. Things Fall Apart by Chinua Achebe, "The Metamorphosis" by Franz Kafka, and "A Very Old Man with Enormous Wings" by Gabriel Garcia Marquez, support this idea by showing us some illustrations of characters who think and act irrationally.
Okonkwo, the main character of Things Fall Apart, displays numerous signs of human irrationality. His biggest flaw is that he is terrified of looking weak, like his father. This irrational and excessive fear of being associated with his father causes him to think and do exactly the opposite of what his father did. He lets his fear control everything that he does. It is hard to understand how a person can grow and survive when he lives constantly under irrational fear.
His efforts to be unlike his father cause him unhappiness and constant dissatisfaction.
Okonkwo's irrationality drives him to violence and bravado, to oppose anything that he perceives as weak, soft, and unmanly, like his father. He displays no emotion, even toward his family. He is fond of his daughter, Enzinma, and Ikemefuna, a boy who is placed by the clan in his house, but he never shows any open affection toward them. Other characters in the story let their barriers down occasionally and let their emotions be seen freely, but not Okonkwo. Trying to hold back his emotion his entire life is an irrational behavior.
One of the biggest displays of his irrationality is his murder of Ikemefuna, a boy to whom he grows attached, so that he would not be seen as weak. "Okonkwo drew his machete and cut him down.