Scientifically valid, practically invalid
In a recent episode of EconTalk, Phil Rosenzweig describes how the artificial conditions necessary to make experiments scientifically valid can also make the results practically invalid.
Rosenzweig discusses experiments designed to study decision making. In order to make clean comparisons, subjects are presented with discrete choices over which they have no control. They cannot look for more options or exercise any other form of agency. The result is an experiment that is easy to analyze and easy to publish, but so unrealistic as to tell us little about real-world decision making.
In his book Left Brain, Right Stuff, Rosenzweig quotes Philip Tetlock's summary:
Much mischief can be wrought by transplanting this hypothesis-testing logic, which flourishes in controlled lab settings, into the hurly-burly of real-world settings where ceteris paribus never is, and never can be, satisfied.