I have only gone down once and that was when I turned onto a side street not realizing that it had a fresh layer of gravel put down by the city road people. I was down in seconds. My closest call was when a friend riding too fast on a steep winding section of road crossed over into oncoming traffic and forced a driver coming up the hill into my lane. I had to clamp down on my brakes and head for the 12-inch shoulder and hope for the best. My tubular tire came off the rim but I did not go off the road and fall several hundred feet nor did I hit the oncoming car.
Wet surfaces usually contain a mixture of water and oil and so are exceedingly slippery. Same goes for pavement with a thick coating of leaves. On many roads with curves I need to anticipate drivers coming in the opposite direction at too high a speed for their ability to stay in their lane and I adjust my own speed accordingly. On many downhill sections I will let a platoon of cars go past and wait a 3-4 minutes before heading down so as to minimize the liklihood of catching up to them and needing to use my brakes - though less of a concern with newer bikes with disc brakes and clincher tires.
I am well aware that as one gets older any injuries take longer to heal and so I am more cautious about what I do and more inclined to avoid unnecessary risk taking. Riding on wet pavement or in heavy traffic are risks I no longer take. It is consistent with my long held belief in not taking a risk if I could not afford to be wrong, i.e. survive.