  A strictly time-domain formulation of the log-sensitivity of the error signal
to structured plant uncertainty is presented and analyzed through simple but
representative classical and quantum systems. Results demonstrate that across a
wide range of physical systems, maximization of performance (minimization of
the error signal) asymptotically or at a specific time comes at the cost of
increased log-sensitivity, implying a time-domain constraint analogous to the
frequency-domain identity $\mathbf{S(s) + T(s) = I}$. While of limited value in
classical problems based on asymptotic stabilization or tracking, such a
time-domain formulation is valuable in assessing the reduced robustness cost
concomitant with high-fidelity quantum control schemes predicated on time-based
performance measures.
