Efficiency trades off against resiliency - Made of Bugs
Past some point, making a system more efficient will mean making it less resilient, and, conversely, building in robustness tends to make a system less efficient (at least in the short run).
This is true of software, networks, and organisations.
When we set metrics or goals for a system or a team or an organization that ask for efficiency, let us be aware that, absent countervailing pressures, we are probably also asking for the system to become more brittle and fragile, too.