I dunno. One of the things you pick up when you fix things regularly is when something should be marked as NFR - Not For Resuscitation. There are the clear faults where a component or physical thing has failed; not always quick to find, but unambiguous when you do and unambiguously fixed thereafter. There are the clear beyond economic repair units, where the damage is too widespread, faults have cascaded, or parts are unobtainable/too expensive. And then there are the heartsinks, which sort of limp on after you've sort of fixed the problem, but you're not quite sure that you have and the behaviour isn't solid enough to let you be confident that you fully understand what's going on. When you factor in your time and effort - and in particular, what else you could be doing instead - that final category of repairs gets old really quickly,
Nobody likes walking away from something where there's a chance that one more push will ensure victory and if you're a hobbyist who enjoys the chase then these things can be kept going for a long time (I spent more than a year on a mammothly complicated colour dual-standard buggered TV chassis when I was a kid; it was great fun and I learned a lot. It never worked.) Later in life, not so much.
I guess everyone who follows EEVBlog does so because they have a passion for electronics, whether or not it's their job as well. Sorting out hard problems can be addictive (I remmeber a really good column called In Your Workshop in one of the UK TV technical magazines, which specialised in that.)
Sometimes, though, you have to look at a quivering patient on the table, flip the switch and throw the sheet over its head. There's always another.