Okonkwo was raised by a father who was lazy and ineffective in a tribe where masculine prowess and accomplishment had supreme value. In contrast, the tribe holds loathing for men who are agabala, which means weak and lazy. Okonkwo had a deep inner terror that he would be like his father: weak, ineffective, lazy, unmanly, despised. No one knew of his inner terror. The tribe admired him, respected him, awarded him with honors, recognized him as the best and fiercest warrior in the tribe.
Okonkwo had long since conquered the image of his father's failure and proven himself to be a leading man in the tribe. Yet the spectre of his father's despised traits and his terror of being similar continued to drive him and compel him to continually act in heartless and reckless ways that proved his manhood. It was because of this driven compulsion to prove himself over and over and unendingly that Okonkwo made rash choices and risky decisions--actually, Okonkwo’s actions must be said to be guided less by reasoned decisions as by compulsions of terrified impulse. He might be likened to the falcon and his reasoning self to the falconer in the quote:
The falcon cannot hear the falconer;
Things fall apart; the center cannot hold;
Mere anarchy is loosed upon the world.
Because he, like the falcon, could not act based on truth and tribal reasonableness, he fell apart, his center could not hold, he unleashed anarchy upon his world. Okonkwo's tragic and fatal flaw of being compelled by driving terror lead to his fatal end as a tragic hero.