Once, when I was about 20 my toenail started to hurt, I looked at it and it didn't seem different, but I noticed that the toenail was a teensy bit in the skin. I got the nail scissors out and cut the nail. It was like peeling open a can of ready-roll pastries-there was a small pause and then a pop as a small river of brown pus rolled out over my toe. I spent a happy half hour or so cleaning under the nail, and then over the course of about 6 months it grew out. I was almost sad when I said goodbye to the last thickened nasty toenail.
It has never happened again despite my best efforts to the contrary