A manager finds the output where marginal profit is zero and stops there. What has been skipped, and what could go wrong?

A. The second-order condition, since zero marks three possibilities

Flatness is shared by peaks and troughs, so the sign of the second derivative is what tells them apart, and a manager who skips it can confidently produce at the profit minimum. The FOC finds candidates and the SOC selects among them, which is why the ritual has two steps.