Why do plotted lineweights sometimes differ from what you see on screen?

[indiancad]

A drawing may look properly organized with different lineweights assigned to layers, but the final PDF or printed output can look completely different. Some lines appear too thick, while others become difficult to distinguish.

One possible cause is a mismatch between layer lineweight settings and CTB/STB plot style configurations. The PLOT settings and selected plot style table can override the appearance you expect.

When your plotted output doesn't match the drawing display, what do you check first: layer properties, CTB/STB settings, or plot configuration? Have you encountered any less obvious causes?