Expertise in a medical specialty requires countless hours of learning and practice and a combination of neural plasticity and contextual case experience resulting in advanced gestalt clinical reasoning. This holistic thinking assimilates complex segmented information and is advantageous for timely clinical decisionâmaking in the emergency department and paediatric or neonatal intensive care units. However, the same agile reasoning that is essential acutely may be at odds with the slow deliberative thought required for ethical reasoning and weighing the probability of patient morbidity. Recent studies suggest that inadequate ethical decisionâmaking results in increased morbidity for patients and that clinical ethics consultation may reduce the inappropriate use of lifeâsustaining treatment. Behavioural psychology research suggests there are two systems of thinking â fast and slow â that control our thoughts and therefore our actions. The problem for experienced clinicians is that fast thinking, which is instinctual and reflexive, is particularly vulnerable to experiential biases or assumptions. While it has significant utility for clinical reasoning when timely life and death decisions are crucial, I contend it may simultaneously undermine the deliberative slow thought required for ethical reasoning to determine appropriate therapeutic interventions that reduce future patient morbidity. Whilst healthâcare providers generally make excellent therapeutic choices leading to good outcomes, a type of substitutive thinking that conflates clinical reasoning and ethical deliberation in acute decisionâmaking may impinge on therapeutic relationships, have adverse effects on patient outcomes and inflict lifelong burdens on some children and their families.