As a non-pilot, albeit a reasonably well-informed one I would like to think, I can't understand how situations like this arise.
We are talking about two experienced pilots (or at least one very experienced one). They will have taken off many times and know their machine backwards. They should know weights, thrust settings and speeds like the backs of their hands.
An error of input is understandable but surely when it throws up a thrust setting of 81% for a four-hour flight with a full load, when previously it came up say with 90+ % for a Palma or Ibiza, alarm bells should start ringing in their heads? Especially as there are two of them!
Or am I missing something?