Full Idea
For explanation simple laws must have the same form when they act together as when they act singly. ..But then what the law states cannot literally be true, for the consequences that occur if it acts alone are not what occurs when they act in combination.
Gist of Idea
Simple laws have quite different outcomes when they act in combinations
Source
Nancy Cartwright (How the Laws of Physics Lie [1983], 3.6)
Book Reference
Cartwright,Nancy: 'How the Laws of Physics Lie' [OUP 2002], p.72
A Reaction
This is Cartwright's basic thesis. Her point is that the laws 'lie', because they claim to predict a particular outcome which never ever actually occurs. She says we could know all the laws, and still not be able to explain anything.