Okonkwo's error
Achebe's protagonist is strong, industrious and respected — and destroyed by his terror of resembling his gentle father. He mistakes rigidity for strength.
Culture under pressure
Things Fall Apart also shows a whole society unable to bend, and therefore breaking. The parallel for a man is any identity that cannot absorb new information.
Flexible spine, fixed values
Hold values fixed and methods loose. A man who changes his principles with the wind is weak; a man who cannot change his methods is brittle.