It’s not so much that we cannot believe it as that we did not expect it. It refers to things outside of our frame of reference or expectation.
This is usually because it’s very rare or really unlikely.
It would be more acuate to say I did not account for it.
Disruption works this way. So does the outbreak of epidemics and sports upsets.
Sure, it’s not sustainable to expect a mugger behind every bush. This leaves us with two viable options. Either we accept the risks we cannot plan for and the circumstances that are hard to predict, or we create processes that do the work for us.
The first requires a willingness to accept. Blame shifting is not productive. Your reality is beyond your control, and you have chosen to accept this.
The second requires hard work and continuous improvement. It won’t add value often, but when it does, it will be significant.
So really, it’s not unbelievable. It’s just not important enough.