Simple rules are a way of reducing a complex problem with many unknowns to simpler tradeoffs, like yes or no, above or below, or left or right. It’s as in traffic: in the vast majority of situations, driving on the correct side of the road is good advice. Or reducing your speed in misty weather.
We may need, for example, to modify the application of Basel II in the United States, where permissible under the Basel agreement; negotiate further changes in the international agreement itself; or change the way the current capital rules are applied to institutions that do not adopt the new standard.