In all the years that I've been doing photography I've only had one serious accident.
I was in the mountains in northern Georgia on a spring morning just after dawn. I stopped to photograph a lovely valley shrouded in mist. It was my first shot of the day, so I open the trunk of the car, and set up the tripod beside me to prepare to hike into the field overloking the valley. I took the camera and lens I wanted (a Rollei 6008 with 180mm lens) out of the bag and put it on the tripod head (a screw type QR system).
Just as I was doing so I realized that I wanted a few extra rolls of film (remember film?), and so reached back into the trunk to stuff some in a pocket of my shooting vest.
As I looked up I saw that the mist was rapidly dissipating, and so quickly grabbed the tripod and slung it over my shoulder.
At this point the Rollei and its attached lens described an arc through the air, landing in the middle of the concrete road, about 15 feet away. I had neglected to tighten the QR plate knob.
The camera survived, but the meter prism and lens were toast. About a $5,000 mistake.
Worst of all, I missed the shot I wanted.
The next day I ordered lever clamp QR plates for all my tripods and have used nothing else since.