Not sure I would agree with that. The knife was definitely a requirement in that environment. Making fire was work, but they got it figured out. No knife would've left them defenseless and unable to finally protect their feet the way they did. Maybe the fire kept the hyenas away, maybe not.

Maybe pot and knife, but firestarter? Not if you know what you are up to.

No sale.
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The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)