Doppelgangers scare us because they reflect ourselves

In horror stories of doubles, there is always a sense that the doppelganger could be you, that your personality is fragile and now you are acting in strange ways. Doppelgangers are close to us, but are not us. They are the parts of ourselves we have repressed or kept hidden.

References

Naomi Klein explores this idea in Doppelganger-by-Naomi-Klein-2023