This idea can be challenging to entertain (it was for me). But I think it's an interesting concept to at least think about with an open mind. Just don't take it too literally.
The idea here is that what we see in others is often what we see in ourselves. The qualities we most admire in others are often those we admire about ourselves. Likewise, what irritates us in others may be what we don’t like about ourselves. What you judge in someone else, you are actually judging in yourself.
Therefore, what you notice and what irritates you in others can teach you important things about yourself, things you may not be aware of. In a way, people can be like a mirror for you to help you to learn more about yourself.
© Henrik Edberg