In times of trouble, ask "What is the user problem that we are trying to solve?"

Emphasis here on "...PROBLEM WE ARE TRYING TO SOLVE".  We easily get caught up in fitting buttons and fields on screens etc.  But often - even after requirements have been detailed - we loose sight of the fact that we are trying to solve business and human problems with the functions and information that we are designing.  Asking this question helps reorient the project back toward what is important. When elevated to a mantra, other teams on the project start asking the question and you know an attitude change has been affected.