Dentist: “You have multiple cavities.”
Patient: “That’s ridiculous! You always told me that brushing my teeth prevents cavities. I brush my teeth every night. Therefore, I can’t possibly have cavities.”
Dentist: “It is true that brushing your teeth has been proven to help prevent cavities. However, in your particular case, there could be other factors negating the positive effects of brushing your teeth, e.g. you aren’t brushing long or thoroughly enough.”
In the above scenario, the patient thinks that simply because they brush their teeth, they are guaranteed not to get a cavity, i.e. the patient thinks that there is a simple, causal relationship between brushing teeth and not getting cavities. In reality, only brushing one’s teeth thoroughly and completely, for a sufficient amount of time, with a proper brush, etc. will prevent cavities. In other words, there are multiple factors at play that determine whether brushing one’s teeth will produce the desired effect or not.