Specifying the task and the desired behavior precisely; the scarce skill once raw model capability is commoditized.
Tensions
Yao Shunyu argues that on paper everyone's models look similar, so the real differentiation comes from how clearly you define the problem and the behavior you want, and much of the observed gap between models traces back to this unglamorous definition work rather than to cleverness. It is the upstream counterpart to evaluation: a poorly defined problem cannot be evaluated honestly.