Confused by Outlet Wiring
In my bedroom I have an outlet on the wall next to my closet door. I am pretty sure that -- long ago -- one of the two lights switch near the entrance to the room controlled the lower of the two sockets on that outlet, but at some point someone disconnected the light switch so now both of the sockets work regardless of the position of the light switch. (I can't find any outlet and/or socket controlled by the light switch.)
I decided I wanted an outlet inside my closet, which seemed like a simple enough task. I've done plenty of home improvement tasks like this, including other outlet upgrades, etc.
I cut the power at the breaker, then removed the faceplate from the existing outlet and then unscrewed it and found that there are two heavy gauge wires going into the outlet, with the hots and the neutrals attached where you'd expect on the left and right, and the ground wires from each spliced together before attaching to the ground screw on the bottom. I removed one hot and one neutral and undid the ground splice, then pushed that up through the hole in the back of the gang box.
I found the stud on the inside of the closet opposite where the existing outlet is, measured about four inches above it so I wouldn't hit the existing outlet, and cut through the drywall to make a hole big enough for a 1-gang box. Inside I found the wire I'd pushed through, connected it to my new outlet, then went and flipped the breaker. The original outlet worked fine, but the new outlet was completely dead.
My assumption was that there had to be something with the original light switch wiring that was the problem, so I decided to do more research and try again later, but then realized that with the new outlet wired in place, there was no power to a completely different outlet (on the same wall). So I cut the power again, removed the wires from the new outlet and put them back exactly the way they were and now everything is back to working, but I cannot understand (a) why what I attempted failed and (b) why the completely separate outlet stopped working. Anything obvious I'm missing here?