Delivering Unwelcome Information
People are reluctant to deliver bad news, and tend to avoid considering how to go about it. As a result, they end up delivering an ill-conceived message at an inopportune time. At one extreme, there's a blunt and callous delivery, and at the other is a message so vague that the other party doesn't get a clear sense of what you're trying to say.
Timing is important: the longer you wait, the more likely issues will fester. However, consider whether the other person is receptive at the time: if a person is having a terrible day, or is upset about other things, bringing them bad news could make you the outlet for their general sense of frustration.
Also, bad news is best broken in person, and in private.
Depending on the person and the situation, providing a "set up" before delivering the bad news may help soften the blow - or it may be better to deliver the bad news up front and provide explanations afterward.
Delivering bad news does not engender goodwill: your goal is to communicate the message, get acceptance and understanding, and minimize the damage to the relationship.