Ghosts, although incapable of harming people directly, can diminish the three fires within a person's body, causing their fortunes to wane and bad luck to follow. In minor cases, this leads to severe illness; in the worst cases, it can lead to the disintegration of a family and loss of life.
However, this does not mean it can succeed with just anyone; the other person's fortunes must already be in a weakened state for the ghost to be able to give them a nudge, exacerbating the situation. If the person's fortunes are strong, not only would the ghost fail to diminish it, but it could potentially get burnt by the individual's three fires instead—such an outcome would be lucky for the ghost.
Yang Xuejiao, having recently lost her daughter and now her husband, is experiencing a decline in her fortunes, a sudden upheaval in her life.
With her misfortunes at their peak and her three fires naturally dim, this provided Fang Yunlou with an opportunity to get close to her.