not every doctor agrees about these ideas. some doctors think that the link between good flossing habits and good heart health is only a coincidence. a coincidence is the occurrence of two or more events at one time apparently by mere chance. the incidence of these events is completely random, as they do not admit of any reliable cause and effect relationship between them. for example, every time i wash my car, i somehow change the weather. this is only a coincidence. likewise, some doctors think that people who have bad flossing habits just happen to also have heart problems, and people who have good flossing habit just happen to have healthy hearts.