You won't believe this but: I was wrong.

I said that I had never had a sealed bearing bottom bracket come loose.

It just happened while I was up on the side of a hill.

The bike started missing shifts on the crank and I assumed it was the cable stretching and kept adjusting it.

Soon it wouldn't get into the big ring.

I stopped to see what was wrong 11 miles from home and saw that the right side had unscrewed almost all of the way out. This caused the left side to screw all the way in.

If you were using an old fashion open ball assembly it would have dropped all the balls out and you'd have been totally broken down. But it would still work in a slow gear and I managed to make it home for repairs.

30 minutes later and all is well that ends well.