The Second Line Cannot Challenge What It Cannot Evaluate
The three lines model rests on an assumption that holds well in financial risk and poorly in cyber. It assumes the second line can evaluate the first line's work independently, which requires the second line to understand that work at least as well as the people doing it. In model risk management at a bank, that assumption is satisfied by staffing. The independent review function employs people who can re-derive a model's output and disagree with it on technical grounds.