Why do fortune tellers say that girls' single eyelids are not good?

Because according to folk superstition,

Single and double belong to yin and yang eyes.

Is to see the eyes of ghosts and gods

Actually, don't mind, how many people really have yin and yang eyes? Oh, like this, it is usually inherited from ancestors ~ and the yin and yang eyes are not necessarily a single pair.

Don't be too superstitious.