I just lighted upon this sentence in a book:
Academic attention has focused in two main directions.
This sentence reads slightly odd to me, because although "direction" needs the directional preposition "in", "focus" usually collocates with "on". The only context in which "focus" is followed by in, as far as I know, would be such sentences as:
You need to stay focused in the game.
Try to focus in the book on that particular chapter.
This, of course, is a different story.
The first sentence makes me wonder about the rules governing preposition choices in a situation like this. Are there any rules that say, for example, "prepositional verbs take precedence and cannot change their prepositions based on the object" (which means that sentence from a book is stilted and should've had better editing) or "prepositional phrases rule sometimes" (which means that sentence is okay)?
How does that sentence strike you?