This is a difficult question to answer without more information. How did this happen could refer to any number of things, so it's impossible to give a comprehensive answer. However, we can look at some possible scenarios and try to piece together an explanation.
One possibility is that whatever happened was the result of human error. This could mean that someone made a mistake while performing a task or neglected to do something that they should have done. For example, if a machine broke down and caused an accident, it might be because someone didn't properly maintain it or failed to follow safety procedures.
Another possibility is that the event was due to natural causes beyond our control. This could include things like severe weather conditions or unexpected mechanical failures. In these cases, it may not be possible to determine exactly how or why the event occurred, but we can still investigate what went wrong and take steps to prevent similar incidents from happening in the future.
Of course, there are also situations where foul play is involved. If something happened as the result of criminal activity, then there would be different investigation protocols in place. In this case, how did this happen would refer specifically to how the perpetrator(s) managed to pull off the crime without getting caught.
Ultimately, the best way to figure out how something happened is to conduct a thorough investigation and collect as much evidence as possible. By piecing together all of the available information, we can often come up with a pretty good idea of what happened and why.