Sometimes its a systems problem, sometimes procedures, sometimes maintenance. Too often it's simply finger trouble. This Smithsonian video relates five instances where fatal crashes can be traced back to simple pilot mistakes. The ability to avoid these crashes was in the hands of the crew, but they failed to take the right action. It should be a reminder to all air crew out there that we are, in most cases, the weakest link in the safety chain. Did you really keep a good lookout? Did you interpret that instrument properly? Did you understand the DAP? If it can happen to professionals it can happen to anyone.