Realists argue that mature theories enjoying predictive success are approximately and partially true, and that the parts of the theory necessary to this success are retained through theory-change and worthy of belief. I examine the paradigmatic case of the novel prediction of a white spot in the shadow of a circular object, drawn from Fresnel's wave theory of light by Poisson in 1819. It reveals two problems in this defence of realism: predictive success needs theoretical idealizations and fictions on the one hand, and may be obtained by using different parts of the same theory on the other hand.
I maintain that these two problems are not limited to the case of the white spot, but common features of predictive success. It shows that the no-miracle argument by itself cannot prove more than a \textit{skeptical realism}, the claim that we cannot know which parts of theories are true. I conclude by examining if Hacking's manipulability arguments can be of any help to go beyond this position
