Think professional chess players. While prepping they can spend very long hours playing/studding high level chess but tournaments are another level. Challenging is fun, the limits of human ability are always stressful. People can run for 11 hours in an ultra marathon but they can’t do it at 13+ mph pace of a half marathon.
While I'm doing the task: 1) Do I have to hold 15 interdependencies in my head? 2) Is this something I did a million times in the past and do I already know exactly what the failure modes look like? 3) Is this something high-stress, e.g., is this the big project that's supposed to make my team look good or net me a promotion?
Wiring in a UI for a sophisticated CRUD can take 10 hours but it doesn't _really_ have that many interfaces, I've done it a million times, and nobody getes excited about it. It's just something you do.
Building a billing pipeline for a product is something I've never done before, is very-high-stakes for the business, and can go wrong in a bazillion ways, many of which are not my fault. There's no way I can imagine getting more than an hour or two of work on this per day.
but what about a hard problem that you do not make any progress on and you are sure what you did should solve it and what is wrong, why is it not working? You can't say it's uninteresting, but it is debilitating.
Annual tax return? Expense reclaim forms? Administrative faculty meetings? - All so bad that the most productive folks can turn into procrastinators.