Well isn't there a ruling in aircraft design and safety, that you calculate the probability of a certain failure and judge by its reoccurence if it was just random, or more than likely systematic?
I think i read this in context to the two MAX planes crashing in the exact same way. The first one was ruled as maybe just being some very very freak thing to happen, but it happening twice made it entirely implausible to be without systematic cause.
And well now it is happening twice in a few years with Boeing that weird things happen twice in a row with little time in between in relation to critical security flaws.