Virtually every accident comprises a sequence of events; each sequence is an "opportunity" to prevent the accident - assuming you know the accident is happening.
...or about to happen
if this or
that stays the same. It's like leaving a glass jar on the floor with small kids in the house. They can run into it or not, and if they do they can hurt themselves or not, and you can assume they're on another room and the chance is minimal, etc... but the "opportunity" is there isn't it?