Me tooMy MCL tear was the same story. I (then almost 40) was in a semi-private all day lesson where everyone else was 16 and wanted to ski trees in heavy new snow. It was the beginning of the season, I was on a pair of demo skis--the heavy steel ones (I forget the brand--it wasn't Vokl, but somehow "V" sticks in my mind) which they didn't have in my size (which ego probably had asked for 5-10 cm too long to begin with--that was early in the whole shaped ski revolution when size mattered) so the skis were at least 10-20 cm too long.
After a few hours, my legs were completely thrashed, and I had concluded that at the end of the current run, I was going to quit, and let the rest of them finish the lesson without me (my lesson already having included crash, hunt for ski). I was ten yards from the cat track at the end of the trees (safety) when I crashed.
I still get intermittent knee pain eight years later.
New theory: (1) when your body says stop, sometimes you need to listen instead of negotiate (this isn't situps); (2) injury ski wrecks are like the post-mortem on plane crashes--several contributing factors go wrong, and then add fatigue and challenging conditions and boom; (3) when you're tired, ski something easy. That's why the resorts are using our ticket money on all those grooming machines.