More than anything I wish people would stop making posts in relation to possible human factors that this, that or the other is "inconceivable".
There are many, many "inconceivable" accidents filling the history books, and each one generally teaches us something new, or reinforces the importance of something else. How can any of us say with any degree of certainty at this point, that we are not all about to learn something brand new as a result of this incident?
I'm not suggesting in any way what the cause/causes of this accident may be, but stop fooling yourselves that humans are infallible and that training, procedures and automation are going to save your ass.