What is the tragic flaw of Okownkwo that leads him to be a tragic hero in Achebe's Things Fall Apart?

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:

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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.