An example of a failure to acknowledge reality leading to bad results: the whole standardized test debate with students.
There are a number of factors that could lead to good or bad test scores. The quality of teachers, the aptitude of students, the commitment by parents. All of these factors are necessary for students to be succeeding at learning. But how do we test this? An quick (though imperfect way) is the standardized tests.
These standardized tests are meant to be a benchmark, a way to indicate how much students have learned.
Those that criticize the use of these tests do have a point that they are not all that good at determining if learning is going on, as well as the fact that "teaching to the test" is a common tactic used by some teachers/schools.
There is a problem though. What alternative benchmark do we have to work with? Usually, this is where the conversations stops, because opponents have no solutions.