Final answer:
Foster's controversial claim is that all stories are interconnected and that there are no completely original stories, as they all share common themes and are influenced by one another through intertextuality.
Step-by-step explanation:
The claim that Foster makes about stories in general, which could be considered slightly controversial, is that all stories are interconnected in some way. Foster argues that various narratives, themes, and elements of storytelling recur throughout literature, implying that there are no truly original stories. This idea is often encapsulated in the concept of intertextuality, which posits that texts - literary works, in this case - are shaped by references and transformations of other texts.
In summary, Foster's claim is that all stories share common elements and are influenced by each other, rather than being completely original, isolated creations. This perspective can generate lively discussions about the nature of creativity and originality in storytelling.