Full Idea
You can't think a plan of action unless you can think how the world would be if the action were to succeed; and thinking the world will be such and such if all goes well is thinking the kind of thing that can be true or false.
Gist of Idea
Before you can plan action, you must decide on the truth of your estimate of success
Source
Jerry A. Fodor (LOT 2 [2008], Ch.1)
Book Reference
Fodor,Jerry A.: 'LOT 2: the Language of Thought Revisited' [OUP 2008], p.13
A Reaction
This is part of Fodor's attack on the pragmatic view of concepts (that they should be fully understood in terms of action, rather than of thought). I take Fodor to be blatantly correct. This is counterfactual thinking.