There is an interesting concept in psychology called "Loving others is also knowing oneself." It suggests that ultimately, people tend to love someone who is highly similar to themselves. Even if two individuals appear very different in external personality and behavior, maintaining a long-term stable relationship requires that their underlying personalities share the same fundamental traits. Here, "fundamental traits" refer to a person's relatively stable values, basic attitudes towards intimate relationships, emotional regulation styles, and fundamental views of the world and oneself. Love can change and flow, but these deep structures are difficult to alter, and they determine whether a relationship can truly last long-term.