Why is confidentiality important and when might it be broken?

Confidentiality essentially concerns the privacy of a patient's personal/identifiable details, with information only being given on a need-to-know basis to relevant professionals and ensuring the patient is aware of this. It is important because it improves trust, the information given may be sensitive and it is also important when considering safeguarding of vulnerable people (children and older people).
It may be broken if: The patient consents (e.g. for a study), it is of benefit to a patient lacking capacity (e.g. discussing with relatives to act in best interests), it is required by law (e.g. notifiable disease, birth), or it is in the interest of a single person or the general public (HIV, STIs, TB).