The impact of complexity is determined by the activities that are most common

Complexity, in Ousterhout’s sense, is primarily a term related to the difficult of making changes to a system (Complexity is the greatest limitation in software development). As such, the impact of highly complex modules that rarely need to be changed is very low. A rough equation is presented, where $C$ is the complexity of the overall system, $c_p$ is the complexity of any given part, and $t_p$ is the time spent making modifications to that part:
$C={\sum }_p{c}_p{t}_p$

This loose formula carries the corollary that isolating complexity is much the same as eliminating complexity.

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References

Ousterhout, John (2018). A Philosophy of Software Design.