Note that the number of spacetime points at which "I" have looked in a mirror is, relatively speaking, very few. Indeed, most mirrors are not checked most of the time!
This issue is not primarily about the nature of reality. It is also about why "I" am SURE of something. For example, is it a matter of cognitive economy -- performing a probability calculation every time I saw a mirror [How likely is this one to be "magic"?] would be hopelessly laborious? Or is it a matter of social pressure -- "I" am sure that mirrors are not magic because "I" have never met anyone seriously claiming they are outside stories? Or is it that "I" have faith in modern science -- even though "I" know well that scientific theories are always liable to counter-example and are regularly discarded? Or??