Firstly, to clarify what I mean: There are some spells which use mirrors to 'reflect' a curse, psychic attack, or other negative energy back to its source. It is as it sounds, as in a representation of the often nebulous concept of the origin is surrounded by mirrors or reflective objects to represent this purpose. Some versions have the box being enclosed, to symbolize a permanence, and then the entire unit is discarded, symbolic of both letting go of whatever energy had been sent the target's way, as well as expressing that the working should exist in perpetuity, never to be undone by the person who set up the box.
But there is one serious caution: Sometimes a person is the source of their own misery, often without even realizing. Sometimes a person may believe that some string of less-than-ideal life circumstances are the result of a curse, and it causes a bit of an obsession. It results in a lot of negativity coming from that person, about their own life. It may very well compound into something more, as they lose confidence, lose hope, and increase fear. All the while, they convince themselves nothing is going to work out, everything will fail, and more. All of this negativity compounds upon itself, and the person believes that the increased expression of everything must come from elsewhere.
Doing a mirror box, should it work as intended, may very well be reflecting a person's negativity back upon themselves, if they are the source of their own misery, or their own belief in being the target of negative workings is the reason they are experiencing even more unwanted events and circumstances.
These workings are often best used when an actual external source is known, to avoid this possible outcome, if at all possible.
A caution on mirror-boxes