A mass misbelief in the continuation of Moore's law into impossible sub-molecular scales. There is no more low-hanging fruit of "just make the optics more precise to make the lithograph smaller"; every process-node step we're taking now is rather a "side-step" involving solving increasingly-complex puzzles to make the same-sized features do more per molecule. It's code golf, at a hardware level. And as in code golf, there's a pretty low ceiling as to how intricately interwoven features can become. You can't eliminate the fundamental need to have all those features
in the code (circuit) in some sense.
The actual visible effect of this is an economic one: we've gone from spending linearly more marginal CapEx per fab process-node upgrade, to spending geometrically more marginal CapEx. Each process node under 8nm has been twice as costly to design as the one before it. This is untenable.