Let me tell you a story....
I was once doing a job in a factory that made magnetic tape. The whole factory floor was a clean-room. Dust was carefully controlled and everyone in the room had to wear white paper coveralls from head to foot. We were installing a monorail in the ceiling space that fetched the finished tape in huge reels and put it in an automated store. When a worker unloaded a tape from the machine or wanted to load one onto the machine that cut it up and put it on spools, they pressed a button on a box. A light would light up to say the computer knew that they were waiting and that a trolley was on the way. In that box there was a circuit board and on the bottom of the circuit board there was a row of screw terminals to connect to the buttons and the lights, and the signals from the computer. The lights and buttons worked on 24V and the logic worked on 5V. The terminals were about 0.2 inches apart -- twice the distance they are on a Raspberry Pi.
One day I suspected that one of the boards had failed. So I put on my white paper coverall, with the white paper booties and the hood, and I took a screwdriver, a meter and a spare board into the clean room. Sure enough, the board had failed. I was then faced with a conundrum. Do I go back outside, take off the white paper coverall, switch off the power, put the coverall back on and come back inside? Or do I just trust that I know what I am doing and which wires are the dangerous ones, and I can be very careful not to touch something I shouldn't with a wire that I shouldn't? I was young and confident, so I'm sure you can guess which option I chose.
The top of the chip cut my cheek as it went past. The legs are all bent up because I kept it in my wallet for several years as a reminder not to be such an idiot.
Fortunately that was the only component to be damaged and I could swap the chip out of the old board. But I switched the power off first.