It was one misty morning, and apparently it had been misty for hours. That let the dampness seep into everything, including the trike's brakes.
I had always heard/read that bicycle brakes grip less well when they and the wheels' rims are wet. With the trike I found it to be the opposite: they grabbed harder when wet. And I had front-wheel brake only.
That morning I started out on my ride, and was braking as I approached a stop sign a block from home. Before I knew what was happening, I was on the ground with the trike on top of me. It''s not as though I had been flying along at 20 mph, either. Under 10 mph, probably.
Luckily I wasn't hurt, but the thought that flashed through my mind was, "The old gal's developing temperament!"