Struggling with HiPPOs Again

How often do I hear that we don't need to test because "We know our customers" or "We've been in the business for 'X' years" or, my personal favorite "We have come to the conclusion ... "

Coming to a conclusion, based on facts is one thing, but coming to a conclusion based upon personal judgment or intuition without direct testing is something else. I completely understand when time or budgetary constraints come in and the development team is "forced to go to war production with the army design they have." That being said the organization understands that mistakes in preparation have been made and that careful re-thinking of the application must be made. (Often times this re-thinking never occurs until the next hurried release is made. But that's another story.)

So, how does one deal with the HiPPO (HIghest Paid Person's Opinion) problem? It certainly can't be based upon your intuition that testing ought to be done. Ideally you would have a series of examples were the HiPPO had previously been surprised with user responses and be able to leverage that experience. Aside from that I have not had success. I have brought up examples from lecturers and articles to no avail. I would love to read about other's success rates.