Reasonable human behavior is based on doing something for a consequence that is perceived as good. Ethical medical decision-making is based on prioritizing values after understanding the relevant facts. There is an ethical obligation to do no harm. This is especially true in relieving the pain and suffering of dying patients; in these cases, treatment has the risk of contributing to a patient's death. The principle of double effect has been helpful as a moral guide in troubling cases to discern what actions are acceptable, even though the action could lead to an end that would seem as immoral as if the effect were directly intended. This principle, though, is not without problems and critics, and some have pointed out its shortcomings as an ethical guide.