On opinions vs data for UX Design

This is one of the reasons why I don’t put too much trust into opinion-based usability reviews: There’s a lot of guesswork involved, and guessing how humans behave is an endeavor fraught with peril.2 Expert reviews can be helpful, but they are no substitute for actual testing.

(Source: http://ignorethecode.net/blog/2010/08/13/opinions_vs__data/)