Oh man, so many thoughts on this I don't even know where to start. Give my saga on my WJ a skim:
2003 Jeep Grand Cherokee Overland Build I've done lots myself, and sometimes had it drag projects out and cost nearly as much by the time I buy tools etc. (but I always like adding tools to the collection). My recent motor work ended in needing a new long block. Initially I was blaming myself, but all of the info from the post-mortem seem to show we (I) did nothing wrong... but probably shouldn't have poked this particular bear (lots of good intentioned "while I'm in here" maintenance may, or may not have actually been worse for the old motor). Most of the rest I've done, but some stuff I've had done on it when I was too busy with work, or out of town for extended periods of time - and a lot of that I've had to re-do.
So, on the one hand if you look at the total labor I've put in my WJ myself with my friends over the last few months it'd be thousands and thousands and thousands of dollars. On the other hand, it's still not out of the question that "we" caused the engine failure (which has cost me thousands and thousands and thousands of dollars) and we've given up lots of weekends and it's still not running yet - in fact I'm about to go back to work on it. Obviously internal engine work and an actual engine swap are the most extreme version of being a "home mechanic", but the same could apply to lesser projects. Honestly, I consider myself a good wrench (and a couple of my buddies that helped are professional ASE mater mechanics with decades of experience) so it's pretty humbling to say, "maybe I should have just left this one to the pros..."
-TJ