Years ago a guy my dad knew saw I had an interest in electronics whilst I was watching him doing some rewiring for him in a rented property. I was chatting to him and watching as he pulled old rubber and lead covered cables out of walls and from under floorboards. There were two wires sticking out of the plaster where an old two pin socket had been. A red and a black. "Just pull that black wire through Chris" he said. I pulled it touching the stripped end and got about a foot out before it went tight at his end. "Did you feel anything?" he asked me. "No, why?" I replied. "Well at least the live and neutral were wired right on that spur" he replied, "They weren't on the other one"
"It's not live is it?" I asked nervously. He put his neon tester on the red one and it glowed brightly. "Don't be so trusting around mains wiring kid, you'll make 15 that way". I never did find out if he really knew the black was actually a true neutral, or if he winged it.. But I have always checked before touching unknown wiring after that. I remember him throwing me a component once, a capacitor. I instinctively caught it and got a good belt. "Caps hold their charge for ages, don't forget, will you Chris?" Good teacher, old Ted Hopkins