I'm an experienced DIY'er in carpentry and electrical. There's a lot to do in my circa 1854 house. I studied electrical engineering, but my career led to software programming. I'm fascinated by the surprising intricacies of plumbing. (It seems to have so much in common with electrical/electronic design.) I don't have a lot of hands-on plumbing experience. My story below explains why:
In my last hands-on plumbing adventure, I needed to cap off two 1/2" copper pipes to an abandoned fixture. I shut off the nearby valve, cut the pipes, reamed and sanded them clean, applied flux, put on the caps, and proceeded with my new torch. Before the solder would melt, the cap popped off like a gun with a burst of steam. After my pulse settled down, I determined there was just left over water in the pipe. So I cleaned everything and started over. This repeated five (5!) times. Many very bad words and phrases were shouted.
Slightly before burning my house down, I realized that the valve was leaking very slowly. So, I learned to shut of the main valve before doing any work. (I was successful after that.) I also learned that there are probably many more experience-related skills to plumbing than I imagined. So ever since, I've left my torch in its drawer, and instead use my phone to call a pro.