Why do train derailments happen?

Two umbrella categories can be used to describe how and why derailments occur: technological malfunction (which includes machinery which unexpectedly fails and unkempt, dangerous tracks) and human error (such as mistakes made by the conductor or engineer, inattentiveness or otherwise). It should be emphasized that both of these things are bound to happen with time. Humans, even when well trained and highly qualified, are going to make errors. And in a system like our railroad system, technological errors and malfunctions are bound to occasionally take place. In spite of the somewhat inevitable occurrence of these two things, however, derailments still can be largely prevented. When implementing safety technologies it is standard to account for both human error and technological malfunction in the equation. Railroad companies have become known for ignoring these factors as they implement safety technology. A bare minimum of systems safety is not appropriate, because mistakes are bound to overwhelm the system.