This article argues that social workers and the general public need a clear understanding of the distinction between avoidable and unavoidable mistakes in child protection work. The public is understandably distressed when a child dies and is right to demand an inquiry to check the quality of help provided. But a child's death is not proof that any professional was incompetent. Our limited knowledge and the complexity of assessing risk mean that professionals can only make the best judgement on the available evidence. Analysis of forty-five inquiry reports shows that inquiries appreciate this; in 42 per cent of them social workers were not criticized. The analysis however also reveals one persistent error: social workers are slow to revise their judgements. Psychology research indicates that this error is widespread and by no means peculiar to social workers but it means that misjudgements about clients that may have been unavoidable on the limited knowledge available when they were made continue to be accepted despite a growing body of evidence against them. Social workers need a greater acceptance of their fallibility and a willingness to consider that their judgements and decisions are wrong. To change your mind in the light of new information is a sign of good practice, a sign of strength not weakness.