A few years ago, on the Nurburgring, I got turned back for having worn out tires, which was fair enough as even though they were semi slicks, I was sliding all over the place in dry weather.
Being back on road tires there was not much of a point in driving fast, so ran into a guy i used to know and he offered a couple of passenger laps in his really fast car, to which I accepted. He bailed and I could only see him getting on track, but since the track was still very empty and the early morning mist rising, I couldn't resist and took my car out for a gentle lap with my brother.
Halfway through the track, on the only piece of track with a concrete wall, braked on a big oil spill and went sideways into the wall at 100 or 120kmh. Quite lucky to not hurt my brother who was on the side that went against the wall.
The coincidence? That oil spill had been caused by the car I was supposed to be in as a passenger, it had just blown it's engine and dumped a lot of oil downshifting into that corner 30 seconds before.