CP chemistry really is a kind of mysticism.
Sometimes, even couples who have been married for decades might not have CP chemistry when standing together. It's not necessarily people with high attractiveness who have CP chemistry. In some shows, the male and female leads are particularly good-looking, but when they stand together, it feels like they don't match, like they're disdainful of each other, resulting in no CP chemistry. Some male leads are overly greasy; if they weren't handsome, their way of hitting on girls would make people want to call the police. Some female leads have their beautifying filter turned up to the max, always looking innocent and silly. Such pairings also lack CP chemistry.
