It's not just the difficult stuff, but often the mundane, e. g. stability, user friendliness, polish, scalability etc. that takes something from working in a constrained environment to an actual product - it's a chore to work on and a lot less "sexy", with never enough resources allocated to it: We have done all the difficult stuff already, how much more work can this be?

Turns out, a fucking lot.

While I agree with the underlying point, the "Pareto Principle" is "well known" like how "a stitch in time saves nine" is well known. I wish this adage would disappear in scientific circles. It instantly decreases credibility. It's a pet peeve but here's a great example of why: pseudo-scientific grifters.