The authors examine recent arguments purporting to show that mental incompetence (lack of decision-making capacity) is not a necessary condition for intervention in a person's best interests without consent. It is concluded that these arguments fail to show that competent wishes could justifiably be overturned. Nonetheless, it remains an open question whether accounts of decision-making capacity based solely on the notion of understanding and appreciation can adequately deal with various complexities. Different possible ways of resolving these complexities are outlined, all of which need further exploration.