My estimate was predicated on employment. If you don't have your job anymore, then it's of course 0% (and you are well aware of your $0 EV). The complement equals "company ceases to exist" + "banking errors" + "getting laid off without receiving your last paycheck".
I think they meant that usually (90% of the time, say), you (know you) have a ~99.999% chance of getting your paycheck, and sometimes (the other 10%, say) you know you have <50% chance.