The same thing affects business owners, only worse. They often stay in the one job for in excess of ten years or so. The lack of objectivity a normal person can unwittingly suffer after five years in the one place can be profound. It is compounded by the tendency to stop getting out and about, observing the competition. A business can become frozen at a moment in time quite easily.
Customers add to the problem.
They have a tendency to not want to 'rock the boat' and often leave bitter and twisted, having failed to assert their feelings, but silently vowing never to return. My customers tell me they love the place', you're right in the danger zone. There is a way around the problem, though. Very nice.' or similar. The answer to a specific question, phrased like this will enable an answer that is seen by the customer as 'helpful' rather than 'critical'.