Until I got old enough to actually turn a wrench, and then I just experimented and pretended like I knew what I was doing. I fucked up a lot the first few times, but I learned every time I did something wrong and now I'd say on a scale of 1-10 with 1 being jacking up your car and 10 being rebuilding an entire car from scratch I'm about a 7.5.
"It's been my experience that straight-line acceleration is probably the first aspect of automotive performance that any intelligent driver gets bored with." - Peter Gregg