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To understand the physical conditions of various gaseous systems, plasma diagnostics must be performed properly. To that end, it is equally important to have extinction correction performed properly. This means that the physical conditions of the target sources -- the very quantities to be derived via plasma diagnostics -- must be known even before performing extinction correction, because the degree of extinction is usually determined by comparing the observed spectra of the target sources with their theoretically predicted counterparts. One way to resolve this conundrum is to perform both extinction correction and plasma diagnostics together by iteratively seeking a converged solution. In fact, if these analyses are performed self-consistently, a converged solution can be found based solely on well-calibrated line intensities, given the adopted extinction law and the R_V value. However, it is still rare to find these analyses done numerically rigorously from start to finish. In this contribution for the APN 8e conference, we would like to review this convoluted problem and sort out critical issues based on the results of our recent experiments. It appears that the convoluted theoretical and observational progresses exacerbated by the highly numerical nature of these analyses necessitated a number of analytical simplifications to make the problem analytically tractable in the pre-computer era and that such analytical simplifications still remain rampant in the literature today even after ample computational resources became readily available. Hence, the community is encouraged to do away with this old habit of sidestepping numerical calculations, which may have been a necessary evil in the past. This is especially true in the context of spatially-resolved 2-D spectroscopy, which obviously conflicts with the uniformity assumption often blindly inherited from 1-D spectroscopy.