Full Idea
Suppose you find in a hotel room a pack of cards in exactly standard order. Not surprising - maybe it's a new deck, or someone arranged them. Not so. They got that way by being fairly shuffled. The explanation would make the explanandum more surprising.
Gist of Idea
If the well-ordering of a pack of cards was by shuffling, the explanation would make it more surprising
Source
David Lewis (On the Plurality of Worlds [1986], 2.7)
Book Reference
Lewis,David: 'On the Plurality of Worlds' [Blackwell 2001], p.133
A Reaction
[compressed] A lovely Lewisian example, that instantly makes big trouble for the (implausible) view that a cause is something which increases the likelihood of a thing.