Rule #016: Accidents happen on the stage that carelessness set.
I had a doctor who told me, repeatedly, that there's no such thing as an accident. He was pretty old-school, not big on excuses and the like. I never truly agreed with him because, you know, there's always some outside factor that plays into an accident. "I didn't know when I left the bike there that you'd be backing the car out of the garage today!"
After a recent accident involving a cup of tea (not mine) and an iPhone (also not mine) I understood the middle ground which would work: Accidents happen on the stage that carelessness set.
The phone sliding off the lap was not intentional. However, someone who was being more careful might have noticed it sliding and stopped it. Alternately, it would have been more careful to realize that the lap isn't the most secure place for a shiny slidey phone, and to place the phone somewhere else.
The mug of tea underneath the phone was not intentional. However, it would have been more careful to place it further away, to avoid knocking it over, to avoid things falling into it.
It was an accident. But the accident was only allowed to happen because several careless choices were made. The accident can never exist except within the frame of choices which set the stage for the accident to happen.
I, myself, tend to be extremely careful in the same chair. Drinks go on the right, always. Electronics (game controllers, TV remotes, phones, laptops) go on the left, always. I know that I knock over drinks now and then - because I put them within reach, usually in the dark, a careless choice. But knowing that, I exercise care with what might get spilled on and have so far not killed anything.