It could be that NASA scewed up. We will know eventually but NASA has been beating the statistical predicted failure of a shuttle for quite a while now. Contrary to someone else's observation on this thread the shuttle is an engineering marvel. It is, however, very complex and expensive. Recent forays into a next generation vehicle has been haltingly maddening to us who have been involved in such endeavors. This will provide the impetus to develop a safer and cheaper manned launch vehicle.
For now our thoughts should be with the friends and family of the crew and all those dedicated workers who have had a hand in this launch and now recovery operations. It is going to be difficult not to respond emotionally in the early days of many months of work that lies ahead.