Swiss cheese
IF it is true that the frequency of failures on QF aircraft has increased recently (as many who should know maintain is the case on this forum) and IF such increased frequency is caused by declining engineering management (as many who should know also maintain on this forum) then the swiss cheese metaphor is appropriate in this case regardless of how minor any given incident is.
If, on the other hand, engineering problems remain within historical statistical norms and if engineering standards have not deteriorated, then the metaphor is not very useful in this case