As in, I need to be honest with myself as to what I shouldn't bother to try to take on, as well as if a job is starting to look like it's going to be over my head. Cars, for one, have never really been my area of ability. I can change a wiper blade or a burned out headlight, that's about it. I'm only sort of kidding.
Part of the thing with cars is, the level of necessity of the thing itself; like, how fucked up is life going to be if you make the thing worse by N orders of magnitude? The car is pretty integral to the smooth daily function of the family life. So, for me, it's generally best not to "experiment" too much.
I have made headway with appliance repair because the appliances, while important, can usually be lived without for a few days-- and likewise, the logistics of getting someone in to look at them is always a big pain in the ass: Wait several days or a week for an "appointment" that consists of a window, like, "sometime between 10AM and 4PM" (Who came up with that deal? How many folks can just sit around all day waiting for this guy?) and then invariably "we need to order a part" which ends up being another week or two with another all-day "appointment window".
So, I'm like, screw that. I've discovered that many common problems with, say, dishwashers can be researched on the internet, and parts can be found there, too. When it gets into electrical stuff, that's where I tend to hesitate, but most of the mechanical stuff is fairly straightforward to navigate around.