This is almost an automatic response for many of us when someone is sad or upset. We say it out of the best of intentions, to demonstrate our compassion, our sympathy, our sense of having been there. The problem is, it has the unintended effect of shutting the other person down, says Knajdl. "When you say, 'I know how you feel,' the unspoken second part of the thought is, 'and therefore you don't have to go into any detail about it,'" Knajdl says. "It increases the patient's sense of isolation, because it's like telling her you don't want her to talk about it."

Unless you've been treated for the same type of breast cancer, have undergone exactly the same treatment, and had the same response, you really don't know how she feels. "We have no idea what it's like, and it's upsetting to the patient when we act like we do," says Knajdl.

What to say instead: A better approach, according to Knajdl, is to ask something like, "How are your mood and spirits holding up through this?" If the person you're caring for is anxious or sad, this gives her a chance to tell you how she feels, which can be a big relief to someone who's trying to pretend she's doing just fine. And even if she answers that she's holding up pretty well, she'll still feel better that you asked.