There is no such thing as 100% safety and never will be.
Though it rarely is accomplished, 100% safety IS achievable, and is never an accident or coincidence.
Occam suggested that all things being equal, the most simple solution was usually the right one, and that the obvious tended to be the truth. In aviation, that's often not the case, as we live and work in an industry of technical complexity; things are often not what they appear. The autopilot problem may well in fact be a smoldering galley fire, the compressor stall in fact a bird strike, and ground effect in fact not at all a cushion of air, but a reduction in induced drag.
When mishaps occur, sometimes they may be tied together, and sometimes great lessons are learned. Hopefully before any more get tied together. Regulations are often written in blood, meaning that nothing gets changed, no rules get established, until a disaster or a death and public pressure prompts the change; it's always been that way from the early days of flying..from the days with no parachutes or even seat belts, until today.
Several years ago I had an opportunity to be interviewed as part of an investigation into a death in a government operation. I was fairly passionate in my commentary, and not at all candid. Nor in my recommendations. At the end of the discussion, the lead investigator, sitting in a room of other investigators, said to me, "We appreciate your time and attention in this matter. We'll take it under advisement. If anyone else dies, we will be able to see a trend, and then we can do something about it." That really tends to sum up the whole process...and the fact that it is very possible for more than one even to occur and be tied to the same problem.
As an example, we've got another thread going on in this forum about lightening striking a 747. The 747 had to be underneath a thunderstorm for this to occur...and in fact, this was the case. For many years, this was common practice. Not until Delta Flight 191 was lost in Dallas due to windshear and a microburst, was greater pressure put on airlines, regulators, training departments, weather agencies, and others to change policies regarding the discovery, operation around, and respect of thunderstorms and microbursts. It kicked off millions of dollars in studies about microbursts, was a big part of the impetus for changes to modern radar today, and affected the way we all operate. How many aircraft were destroyed, or affected in their daily operations before, with the same common link to this one mishap? Many.
Several years ago, Chevron experienced fuel contamination issue. Suddenly a miriad of mishaps, incidents, and circumstances occured with forced landings, failed engines, engine damage, system damage, etc. Looking for a common cause was indeed important, and can't be disregarded.
I learned to fly in the "old school," so to speak. In older airplanes. I flew old airplanes in which an engine failure wasn't even considered an emergency. Today, we declare an emergency with an engine failure. How do we know that the failure was isolated, that another won't occur? We don't. Recently we saw the loss of a 747 in Colombia...three engines down. When one went, one could reasonably say it's extremely unusual for another to go...but less than a minute later, another did go. And so on. Coincidence? Hardly. Exactly why this occured is irrelevant and it's not my purpose to discuss (it's under investigation)...but the point is that be it several engines on the same airplane, several airplanes at the same airline, several airlines in the same country, or several airplanes around the globe...often as not it's coincidence, but not always.
We can't afford to ever assume it is.
In this case (reference this thread), where several entirely unrelated incidents occured, not linked by the same fuel source, same weather conditions, same geopolitical conditions, same company, same maintenance, same aircraft type, same aircrew training or experience, or any other common thread, in the absence of evidence to the contrary, we see coincidence.
One might rightfully suggest it's somewhat of a stretch to believe in the superstitious "bad things always come in threes" theorem, or that Satan's just playing...it's coincidence. Despite common sense, we also rightfully never stop looking for the connections, learning from each one, so that we don't duplicate it again. Where it does happen again, what we have is failure to learn the first time and that, like creating a safe operation, is never a coincidence.