People always ask me if I was scared of blowing my car up since I did my own turbo install in my apartment garage. I never once was worried since I knew if I installed something wrong it wouldnt run correctly, if it was installed correctly enough to run bad had issues I'd see issues when tuning.
I guess I could see doing a timing belt/chain and getting the alignment/timing off, or install cams wrong, or a bad valve adjustment. Will do you get into that stuff yet?
Either way, double check your work and you're peachy keen.
I've been doing that stuff for years.
Even with timing belts/chains installed wrong, wrong timing, cams installed wrong, etc., the car will usually run shitty or be hard to start initially, without damaging anything. I haven't ever (knock on wood) put a car back together that didn't start right the first try since I've been professionally working on cars - and I've done literally hundreds of timing chains/belts.
Hardest thing to do is camshafts on any of the BMW's, those things are NOT fun to time and you HAVE to use special tools. Again though, I've yet to have any issues with them.
As far as blowing motors though, I've popped my share. This past year on the racebike, I blew a couplea motors up...nothing from any flaws or mistakes in the assembly of the motor, just from beating the ever loving shit out of the motors. That's the way to win races though, and I won a bunch of 'em
In the cars, motors pop from time to time - we're making these things shit out upwards of 1000hp...every once in a while a motor will tap out. Driveline failures are fairly common too (well, not COMMON, but they happen often enough that they aren't unheard of).
A recent PITA I've been dealing with is Ford GT oil pump pulleys...the GT has an external belt-driven oil pump (that's almost fucking IMPOSSIBLE to get to), and apparently it's COMMON for the teeth on the inside of the oil pump drive pulley to shred themselves all to shit and cause the oil pressure to drop to zero. The GT takes LITERALLY close to a half hour just to get it up on a lift, and then you have to take some bolts out of the underbelly, lower the car, adjust the lift arms, lift it back up, take some more bolts out, repeat, repeat - because there are SO many goddamn bolts holding the belly pan on, and some of them are ALWAYS going to be blocked by the lift arms....and then there's only a few inches between the front of the engine and the firewall. When changing out the supercharger pulley, it's standard procedure to remove the whole damn blower off of the engine to swap the pulley, rather than do it on the car. And changing the belt is a NIGHTMARE.