By mentioning that 99% accidents are avoidable, I mean that 1% are the result of chain of events that are either unforeseen or considered to be " To remote to be considered ,financially"
That is " We can make a car that never crashes, but who will buy it?" Bcoz it will be expensive.
All our designs etc are based on some assumptions and condition and maybe once in a while, an unforeseen sequence will result in that assumption being invalid.
Take for example: An incident where in the Pax on he emerg exit wanted to check if he could open the Emerg Exit on Ground before Take off...
or An Extremist or terror activity.
In my part of the world they say... 100% can only be assured by divine power. the rest of us are humans.