Lol.
Back when I was a precision TIG welder I unknowingly had chronic hypoglycemia. I have a hard time thinking logically when my sugars get low, and since I went for many, many years with low sugars I wouldn't get the physiological warning signs of low sugar until after I was in the dumb-as-a-door-nail state.
One day I was making conveyor belt pass-through support brackets that I had made hundreds of times before. It just wasn't coming together like it normally did, it seemed to fight me at every step. Note that this isn't a slot-A fits into channel-A type construction; everything was from scratch from sheet steel. I finish it just before lunch. Eh, it looks ok.
I went to lunch. Ate, and then came back to my work station.
My jaw dropped. I built it inside out and backwards. It was rotated inwards on itself as if you took a shirt and turned it inside out; the silhouette is nearly identical. Entirely inside out, left was right, front was back, etc.
I spent the rest of my shift cutting it all apart and rewelding it the right way.
As I later fount out when I began treatment for Addison's Disease, my blood sugars were dipping dangerously low on a somewhat regular basis. I still have to fight of chronic hypoglycemia, but thankfully my meds keep my sugars from dropping down to the retardation level.